Selected publication list to relative topics of NAsPIII/V activities

First demonstration of electrical injection lasing in the novel dilute nitride Ga(NAsP)/GaP-material system
B. Kunert, S. Reinhard, J. Koch, M. Lampalzer, K. Volz, W. Stolz , Phys. stat. sol. (c) 3 (2006) 614
Quantum well heterostructures (QWH) in the novel dilute nitride Ga(NAsP)/GaP-material system have been grown pseudomorphically strained to GaP-substrate by metal organic vapour phase epitaxy (MOVPE). The high crystalline perfection has been determined by detailed structural analysis applying high-resolution X-ray diffrcation (XRD). The active QWH have been embedded in (AlGa)P/GaP-waveguide structures. Electrical injection lasing has been verified for broad area laser devices at low temperatures (80K – 150K) for the first time in this novel material system.


Direct-band-gap Ga(NAsP)-material system pseudomorphically grown on GaP substrate
B. Kunert, K. Volz, J. Koch, W. Stolz, Appl. Phys. Lett. 88 (2006) 18210
Compressively-strained Ga(NAsP) multi-quantum-well heterostructures (MQWHs) with As-concentration above 85 % have been grown pseudomorphically on GaP-substrates by metalorganic vapour phase epitaxy (MOVPE). Detailed structural analysis applying high-resolution X-ray diffraction (XRD) proves the high crystalline perfection of the samples. Optical spectroscopy appyling photoluminescence (PL) and excitation spectroscopy (PLE) verify the direct-bandgap characteristic of this novel material system. The comparison of the experimental data with elemental calculations via the band anti-crossing (BAC) model demonstrates, that the formation of direct band structure can be understood by the strong bowing of the bandgap energy typical for diluted III-V nitrides.


Near room temperature electrical injection lasing for dilute nitride Ga(NAsP)/GaP-quantum well structures grown by metal organic vapour phase epitaxy
B. Kunert, A. Klehr, S. Reinhard, K. Volz, W. Stolz, Electronic Letters 42, 10 (2006)
Electrical injection lasing has been verified for GaP-based broad area Ga(NAsP)/GaP-single quantum well heterostructures (SQWH) near room temperature for the first time. The lasers have been grown by metal organic vapour phase epitaxy (MOVPE). Due to the comparable lattice constants of this novel material system to that of Si, this novel dilute nitride III/V-laser material might be applied for optoelectronic devices integrated to Si-microelectronics in the future.


Luminescence investigations of the GaP-based dilute nitride Ga(NAsP) material system
B. Kunert, K. Volz, I. Nemeth, W. Stolz, J. of Luminescence 121 (2006) 361
Multi quantum well heterostructures (MQWHs) of the novel Ga(NAsP)/GaP material system have been grown pseudomorphically strained to GaP substrate. The crystalline perfection is verified by transmission electron microscopy (TEM). For As-concentrations in excess of about 70%, a direct band structure and adequate luminescence efficiency for laser device application is observed. Temperature dependent photoluminescence (PL) investigations show the influence of carrier localisation and non-radiative recombination processes typical for dilute nitride materials. With rising N content in the active material the emission wavelength shifts towards longer wavelength, leading to Ga(NAs)/GaP MQW structures with photon energies below the indirect band gap of silicon (Si). At the same time the luminescence intensity drops due to an increase in non-radiative carrier traps and/or structural degradation.


MOVPE growth of the novel direct band gap, diluted nitride Ga(NAsP) material system pseudomorphically strained on GaP-substrate
B. Kunert, K. Volz, J. Koch, W. Stolz, J. of Crystal Growth 298 (2007) 121-125
Multi quantum well heterostructures (MQWHs) in the novel dilute nitride Ga(NAsP)/GaP material system have been grown pseudomorphically strained on GaP-substrate by metal organic vapour phase epitaxy (MOVPE). The group V-incorporation has been investigated into ternary as well as quaternary material systems in order to analyse the incorporation behaviour on growth parameters and crystal composition. The As- and N-incorporation efficiency reveals a strong dependence on the macroscopic lattice strain of the epitaxial layer. Despite the overall complex incorporation behaviour of the group V-atoms, the adjustment of the V/V competition on the crystal surface allows for a control of the solid composition.


Morphology of interior interfaces in the novel dilute nitride Ga(NAsP)/GaP material system
S. Oberhoff 1, B. Kunert 2, T. Torunski 3, K. Volz, W. Stolz, J. of Crystal Growth 298 (2007) 98
A novel method is presented which allows to expose and investigate interior interfaces in the Ga(NAsP)/GaP material system by a combination of highly selective etching and subsequent atomic force microscopy. We demonstrate the selectivity of the chemical etchant and prove that structural information and atomic-scale z-resolution is fully preserved when applying the method. A correlation between MOVPE growth parameters and interior interface morphology is confirmed by subjecting compressively strained and lattice matched Ga(NAsP) material to a growth interruption. The interior interfaces of both materials smoothen during growth interruption, and for the compressively strained Ga(NAsP) we obtain a monolayer-structured morphology. The optimization of this material is very interesting from an application point of view as it has shown electrical injection lasing near room temperature and might be applied for optoelectronic integrated circuits based on Si in the future.


Micorstructural anaylsis of Ga(NAs)/GaP heterostructures
I. Németh, T. Torunski, B. Kunert, W. Stolz, K. Volz, J. of Appl. Phys. 101 (2007)1235424
We have investigated the microstructure of compressively strained Ga(NAs)/GaP quantum wells (QWs) with different N contents. This material system is a promising candidate for future integration of photonics on silicon substrates. N-induced microscopic strain fields are detected applying strain sensitive transmission electron microscopy dark-field (DF-TEM) imaging. Exceeding 7% of N concentration, we find a deterioration of the upper QW interface despite a reduction of the macroscopic strain for compositions with increasing N content. These nitrogen-induced structural characteristics of the ternary alloy are presumably correlated with the optical properties as observed by photoluminescence spectroscopy.


Lasing in optically pumped Ga(NAsP)/GaP heterostructures
S. Borck, S. Chatterjee, B. Kunert, K. Volz, W. Stolz, J. Heber, W.W. Rühle, N.C. Gerhardt, M. R. Hofmann, Appl. Phys. Lett. 89 (2006) 031102
We experimentally investigate the characteristics of light emission of optically excited Ga(NAsP) multiple quantum-well structures grown pseudomorphically on a GaP substrate by metal-organic vapor-phase epitaxy. The emission power as a function of excitation power shows at temperatures from 15  to  200  K a clear threshold after excitation with short laser pulses. The emission spectra become narrow at threshold and shift to higher energies. A well defined mode structure is observed above threshold. Complementary, quasi-steady-state gain measurements using the stripe-length method yield positive modal gain values of up to 10  cm–1 at room temperature, thus validating that the structures show laser action.


Dilute nitride Ga(NAsP)/GaP-heterostructures: toward a material development for novel optoelectronic functionality on Si-substrate
B. Kunert, K. Volz, W. Stolz, Phys. stat. sol. (b) 224 (2007) 2730
The current status of the development of the novel dilute nitride Ga(NAsP)/GaP for the monolithic integration of optoelectronic functionality to Si is summarized from the concept, design and epitaxial optimization to the verification of direct energy gap and the realization of electrical injection laser devices at room temperature.


Si (001) surface preparation for the antiphase domain free heteroepitaxial growth of GaP on Si substrate
B. Kunert, I. Németh, S. Reinhard, K. Volz, W. Stolz, Thin Solid Films 517 (2008) 140
The present paper summarizes results of thermal annealing steps on epitaxially grown Si buffer morphology in dependence of Si offcut angle as well as miscut direction. A Si buffer layer was grown on an undulated Si substrate by vapour phase epitaxy, which provides due to its roughness deliberate off-orientations. An optimized annealing procedure under a hydrogen pressure of 950 mbar was used after growth. Atomic force investigation shows that there is a clear tendency to form bi-atomic steps along both b110N directions as long as the surface miscut is low in angle. For the off-orientations in between these two directions the surface steps delimit mono-layer high terraces. An exact (001) Si substrate with a low miscut of 0.12° towards [1-10] was treated by the same annealing condition. The Si surface is strongly dominated by one kind of sublattice but not completely double-stepped. Using this Si wafer as a substrate for GaP heteroepitaxy by metal organic vapour phase epitaxy, an antiphase domain free GaP layer is achieved after 50 nm of overgrowth, proven by transmission electron microscopy investigation.


In situ verification of single-domain III-V on Si (100) growth via metal-organic vapor phase epitaxy
H. Döscher, T. Hannappel, B. Kunert, A. Beyer, K. Volz, W. Stolz, Appl. Phys. Lett. 93 (2008) 172110
Reflectance anisotropy spectroscopy (RAS) was used in situ for the quantification of antiphase domains on surfaces of thin GaP films deposited onto Si (100) by metal-organic vapor phase epitaxy (MOVPE). The preparation of a single-domain GaP/ Si (100) surface was determined via the analysis of RAS peak intensities in reference to the well-known P-rich surface reconstruction of homoepitaxially grown GaP (100). Both preprocessed Si (100) substrates and MOVPE as-grown GaP/ Si (100) films were also characterized ex situ by atomic force microscopy to identify the formation of mono- and diatomic surface steps and to analyze of the domain distribution, respectively.


Heteroepitaxy of GaP on Si: Correlation of morphology, anti-phase-domain structure and MOVPE growth conditions
I. Nemeth, B. Kunert, W. Stolz, K. Volz, J. of Crystal Growth 310 (2008) 1595
Defect-free GaP growth on exact (0 0 1) Si substrates is an important prerequisite for integrating III/V-based optics with Si-based electronics. In the present paper, dynamic electron diffraction in transmission electron microscopy using specific excitation conditions are exploited to unambiguously identify anti-phase domains (APDs) and anti-phase boundaries (APBs) in GaP. These defects are amongst the most critical and detrimental defects when heteroepitaxially growing III/Vs on Si. The geometry of the APDs is correlated to the Si-wafer morphology prior to the Gal? growth as well as to the Gal? nucleation and growth conditions. It is also demonstrated that APDs intersecting the GaP surface can be seen in the scanning probe surface images of these layers as deep trenches, if a suitable annealing procedure is applied. The GaP growth temperature needs to be high enough to allow for the kinking of the APBs away from the {I I 0} planes. Furthermore, the Si surface area covered by monolayer high islands should be as small as possible to initiate self-annihilation of the APBs. Combining optimized GaP growth with optimized Si surface pretreatment, one can realize APD-free GaP on Si after only 40 nm film growth.


Annealing experiments of the GaP based dilute nitride Ga(NAsP)
B. Kunert, D. Trusheim, V. Voßebüger, K. Volz, W. Stolz, Phys. stat. sol. (a) 205 (2008) 114
The post-growth annealing behaviour of Ga(NAsP) multi quantum well heterostructures (MQWHs) grown pseudomorphically strained to GaP substrate has been investigated. The optical properties as well as the structural crystal quality of the novel dilute nitride show an obvious dependence on the applied annealing temperature. Photoluminescence (PL) measurements reveal a step-like blue shift of the PL peak position in line with an increase of PL intensity with rising annealing temperature, The PL line width decreases to a minimal value for an optimized heating temperature around 800 degrees C. This annealing behaviour of the Ga(NAsP)/GaP-MQWHs up to 850 degrees C is quite typical for a dilute nitride, however, the functional dependence of the integrated intensity above 850 degrees C is unusual. The increase of the PL line width above 850 degrees C suggests a deterioration of the crystalline MQW quality, but transmission electron microscopy (TEM) and high resolution X-ray diffraction (XRD) prove the opposite.


Temperature dependence and physical properties of Ga(NAsP)/GaP semiconductor lasers
J. Chamings, A.R. Adams, S.J. Sweeney, B. Kunert, K. Volz, W. Stolz, Appl. Phys. Let. 93 (2008) 101108
We report on the properties of GaNAsP/GaP lasers which offer a potential route to producing lasers monolithically on silicon. Lasing has been observed over a wide temperature range with pulsed threshold current density of 2.5 kA/cm2at 80 K (l=890 nm). Temperature dependence measurements show that the radiative component of the threshold is relatively temperature stable while the overall threshold current is temperature sensitive. A sublinear variation of spontaneous emission versus current coupled with a decrease in external quantum efficiency with increasing temperature and an increase in threshold current with hydrostatic pressure implies that a carrier leakage path is the dominant carrier recombination mechanism.


Ways to quantitatively detect antiphase disorder in GaP films grown on Si(001) by transmission electron microscopy
I. Németh, B. Kunert, W. Stolz, K. Volz, J. of Crystal Growth 310 (2008) 4763
The monolithic integration of GaP-based optoelectronic devices on exact-oriented (001) silicon (Si) substrates requires a defect-free GaP nucleation layer on the Si substrate. Antiphase disorder is a defect that inevitably arises at the GaP–Si interface if mono-atomic steps at the Si surface cannot be avoided. Using dynamic beam intensity simulations in electron microscopy, the present paper depicts transmission electronmicroscopic (TEM) dark field imaging conditions to examine the crystal polarity and hence the antiphase disorder. The methods are refined in such a way that even thin TEM specimens as well as very small (<10nm) antiphase domains can be imaged at low sample tilts. Using the described techniques, one is able to show that the GaP growth temperature and growth mode play an important role in initiating the self-annihilation of antiphase boundaries by making them kink from {110} towards the {111} crystal planes.


Gain characteristics and lasing of Ga(NAsP) multi-quantum well structures
C. Lange, S. Chatterjee, B. Kunert, K. Volz, W. Stolz, W.W. Rühle, N.C. Gerhardt, M.R. Hofmann, Phys. Status Solidi C 6, No. 2, 576-578 (2009)
Lasing is demonstrated for a Ga(NAsP) multi quantumwell structure grown pseudomorphically on GaP using metal-organic vapour-phase epitaxy. For a series of temperatures ranging from 8K to 290 K, the sample emission characteristics are determined. With increasing pump power, a spectral narrowing of the emitted light along with a blue-shift is observed as the lasing threshold is approached. Above the threshold, the emission splits up spectrally into a pattern of clearly distinguishable modes. In addition, the potential of this material concerning roomtemperature lasing is investigated by means of a variable stripe-length experiment, where a modal gain of 10 cm-1is observed.


Band anti-crossing band carrier recombination in dilute nitride phosphide based lasers and light emitting diodes
J. Chamings, S. Ahmed, A.R. Adams, S.J. Sweeney, V.A. Odnoblyudov, C.W. Tu, B. Kunert, W. Stolz, Phys. Status Solidi B 246, No. 3, 527-531 (2009)
We use high pressure techniques to investigate the properties of two classes of “dilute-nitride-phosphide”-based devices; GaNP/GaP light emitting diodes for yellow–amber–red display applications and GaNAsP/GaP lasers, a potential route to producing lasers monolithically on silicon. Based upon high pressure electroluminescence measurements we find that the band anti-crossing (BAC) model reasonably describes the GaN(As)P system based on an average of the nitrogen states. In terms of device characteristics, we find that carrier leakage into the X-minima of GaP reduces the efficiency of GaNP/GaP LEDs with increasing pressure. Lasing has been observed in GaNAsP/GaP devices with a pulsed threshold current density of 2.5 kA/cm2 at 80 K (? = 890 nm). A weak increase in threshold current with hydrostatic pressure indicates that a carrier leakage path that does not involve the GaP X-minima is the dominant carrier recombination mechanism in these devices, in contrast to the LEDs.


Monolithic integration of Ga(NAsP)/(BGa)P multi-quantum well structures on (0 01) silicon substrate by MOVPE
B. Kunert, S. Zinnkann, K.Volz, W. Stolz, J. of Crystal Growth 310 (2008) 4776
The pseudomorphic integration of an active III/V laser material onto Si substrates requires precise strain management of the entire several-mm-thick structure at both room and growth temperature. The incorporation of B into (BGa)P allows for the deposition of tensilely strained layers on the Si substrate in order to strain compensate the highly compressively strained Ga(NAsP) active material system. It is shown that the incorporation efficiency of B under the chosen conditions is unity and that (BGa)P layers with B concentrations high enough to allow for the strain compensation of an active Ga(NAsP) laser material on Si can be grown with excellent structural quality. Therefore, Ga(NAsP)/(BGa)P multiquantum well heterostructures (MQWHs) with high-crystal quality as determined by high-resolution X-ray diffraction (XRD) were pseudomorphically grown on (001) Si substrates. The potential of this material combination to serve as an active optoelectronic device on Si is demonstrated by efficient room-temperature photoluminescence observed from the integrated Ga(NAsP) MQWH.


Influence of annealing on the optical and structural properties of dilute N-containing III/V semiconductor heterostructures
K. Volz, J. Koch, B. Kunert, I. Nemeth, W. Stolz, J. of Crystal Growth 298 (2007) 126
(GaIn)(NAs)/GaAs multi-quantum-well heterostructures are grown by metal organic vapour phase epitaxy at low temperatures and are subsequently annealed in the reactor to optimize optoelectronic properties. Detailed optical and structural studies of the properties of the material, which change upon annealing under different As-stabilization as well as at different temperatures, reveal that there are two major effects of the anneal. The first one is the blue-shift of the fundamental band-gap of the material, which can be attributed to a local change in the group-III environment of the Nitrogen atoms. The second observation is a strong increase in PL intensity and decrease in PL linewidth upon anneal in H2-ambient, which can be attributed to the removal of non-radiative defects in the material. Chain-like N-ordering in growth direction, which induces strong inhomogeneous strain fields in the material and which can be dissolved upon anneal in H2-ambient might also act as one of the main non-radiative recombination centers in the (GaIn)(NAs) material system.


Material Development for Improved 1 eV (GaIn)(NAs) Solar Cell Structures
K. Volz, T. Torunski, D. Lackner, O. Rubel, W. Stolz, C. Baur, S. Müller, F. Dimroth, A.W. Bett, J. Solar Energy Engieering 129 August (2007)
The dilute nitride (GaIn)(NAs) material system grown lattice matched to GaAs or Ge with a
1 eV bandgap is an interesting material for the use in 4-junction solar cells with increased efficiencies. As a result of its metastability, several challenges exist for this material system, which up to now limit the device performance. We performed nanostructural analysis in combination with photoluminescence characterization to optimize the metal organic vapour phase growth as well as the annealing conditions for the quaternary solar cell material. The optimum annealing conditions depend strongly on the In content of the quaternary material. Valence force field calculations of stable N environments in the alloy support the model that the N moves from a Ga rich environment realised during growth into an In rich environment upon annealing. Simultaneously, N induced strain fluctuations, which are detected in the N containing material upon growth are dissolved and the device properties are improved.


FULLSPECTRUM: a new PV wave making more efficient use of the solar spectrum
A. Luque, A. Marti, A. Bett, V.M. Andreev, C. Jaussaud, J.A.M. van Roosmalen, J. Alonso, A. Räuber, G. Strobl, W. Stolz, C. Algora, B. Bitnar, A. Gombert, C. Stanley, P. Wahnon, J.C. Conesa, W.G.J.H.M. van Sark, A. Meijerink, G.P.M. van Klink, K. Barnham, R. Danz, T. Meyer, I. Luque-Heredia, R. Kenny, C. Christofides, G. Sala, P. Benitez Solar Energy Materials and Solar Cells 87 (2005) 467


Specific structural and compositional properties of (GaIn)(NAs) and their influence of optoelectronic device performance
K. Volz, T. Torunski, B. Kunert, O. Rubel, S. Nau, S. Reinhard, W. Stolz, J. Cryst. Growth 272 (2004) 739
We have grown (GaIn)(NAs) lattice-matched bulk as well as compressively strained multi-quantum-well structures by metal-organic vapour-phase epitaxy (MOVPE) suitable for either solar cell or laser applications, respectively. By applying a specific novel TEM dark-field technique columnar strain fields, which are possibly caused by chain-like N ordering in the samples, have been detected. Valence force field calculations show that indeed these chains are energetically stable in Ga(NAs). This chain-like ordering can be dissolved in (GaIn)(NAs), however, upon appropriate annealing, as verified experimentally. On the other hand we find that device performance especially of lasers is limited by carbon impurities in the active (GaIn)(NAs) region of the lasers. The strong affinity of N–C results in an enhanced incorporation of C if the N content in the material is increased. The paper also shows the sources of C incorporation in (GaIn)(NAs) MOVPE growth and how its incorporation can possibly be avoided.


Optimization of annealing conditions of (GaIn)(NAs) for solar cell applications
K. Volz, D. Lackner, I. Németh, B. Kunert, W. Stolz, C. Baur, F. Dimroth, A.W. Bett, J. Cryst. Growth 310 (2008) 2222
 (GaIn)(NAs) lattice matched to GaAs and Ge and having a 1 eV bandgap is a promising candidate for future space and terrestrial multi-junction solar cell structures. The present paper summarizes results of a detailed annealing study of the metastable quaternary alloy having an In content of 8% and a N content of 2.8%. It is shown that photoluminescence (PL) intensity can be taken as a measure of improving minority carrier characteristics in solar cell devices. A direct correlation between PL intensity and quantum efficiency in the (GaIn)(NAs) material system is observed. The annealing conditions, e.g. anneal temperature, time and As-stabilization, have to be adapted to the particular In content of the material in order to initiate the site change of the nitrogen atom from a Ga-rich environment upon growth to an In-rich one after annealing. In addition, the dissolution of chain-like N-ordering in [0 0 1] direction is detected. The greatly enhanced optical performance leads to an improved quantum efficiencies of the (GaIn)(NAs) solar cell material.


MOVPE growth of dilute nitride III/V semiconductors using all liquid metalorganic precursors
K. Volz, J. Koch, F. Höhnsdorf, B. Kunert, W. Stolz, J. of Crystal Growth 311 (2009) 2418
Understanding the growth mechanisms of III/V semiconductors containing dilute amounts of N, like (GaIn)(NAs) is necessary as these materials are promising candidates for the active material in several optoelectronic devices, as lasers and solar cells. As one deals with metastable material systems, growth has to be conducted far away from thermodynamic equilibrium with several characteristics emanating from that. This paper summarizes our present understanding of the growth of dilute nitride materials by metal organic vapour phase epitaxy, using exclusively liquid metalorganic precursors. N- incorporation in III/V semiconductors for Ga(NAs) as a model system is predominantly determined by the competition of the group-V elements. Large dependencies of the N-incorporation on crystal composition as well as on strain are observed. Additionally, there are minor effects of gas-phase reactions of metalorganic precursors. The nitrogen uptake of the quaternary material system (GaIn)(NAs)/GaAs is shown to be dominated by In-induced desorption of the nitrogen from the surface, which results in a decrease of N-content, by increasing growth temperature or lowering growth rate.


Multichip vertical-external-cavity surface-emitting laser: a coherent power scaling scheme
L. Fan, M. Fallahi, J. Hader, A.R. Zakharian, J.V. Moloney, J.T. Murray, R. Bedford, W. Stolz, S.W. Koch, Opt. Lett. 31 (2006) 3612
We propose an efficient coherent power scaling scheme, the multichip vertical-external-cavity surface-emitting laser (VECSEL), in which the waste heat generated in the active region is distributed on multi-VECSEL chips such that the pump level at the thermal rollover is significantly increased. The advantages of this laser are discussed, and the development and demonstration of a two-chip VECSEL operating around 970 nm with over 19 W of output power is presented.


Optimizing the performance of a vertical-cavity surface emitting laser
S. Chatterjee, W. Wohlleben, C. Lange, W. Stolz, M. Motzkus, W.W. Rühle, Appl. Phys. Lett. 89 (2006) 151122
The pulse response of an optically excited vertical-cavity surface-emitting laser is optimized by shaping the pump pulse. The temporal phase and amplitude of the excitation are adjusted by a learning loop with live spectrotemporal monitoring of excitation and emission pulses using a streak camera. The genetic algorithm of the loop is inspired by the optimization occurring in evolution in biology. The pulse response is such decreased from 4.8  to  2  ps. Emission intensity shows strong correlation with the pulse delay and also improves by 63%.


High brightness spectral beam combination of high-power vertical-external-cavity surface-emitting lasers
Y. Kaneda, L. Fan, T.-C. Hsu, N. Peyghambarian, M. Fallahi, A.R. Zakharian J. Hader, J.V. Moloney, W. Stolz, S. Koch, R. Bedford, A. Sevian, L. Glebov, IEEE Photon. Technol. Lett. 18 (2006) 1795
We present the design and fabrication of an optically pumped vertical-external-cavity surface-emitting lasers with double-well resonant periodic gain structure. Each double-well consists of two 4-nm-thick InGaAs strained quantum wells. The double-well provides optimum overlap between the quantum wells and the antinodes of the standing wave of laser signal at high-power and high-temperature operation. The structure is more tolerant to variation of the growth, processing, and operating temperature for maintaining high modal gain. For a 230-µm diameter pump spot, over 4-W continuous-wave output with a slope efficiency of 39% is demonstrated at 30°C without thermal rollover.


Tunable watt-level blue-green vertical-external-cavity surface-emitting lasers by intracavity frequency doubling
Li Fan, T.C. Hsu, M. Fallahi, J.T. Murray, R. Bedford, Y. Kaneda, J. Hader, A.R. Zakharian, J.V. Moloney, S.W. Koch, W. Stolz, Appl. Phys. Lett. 88 (2006) 251117
We report on the development and the demonstration of a tunable, watt-level, blue-green, linearly polarized vertical-external-cavity surface-emitting lasers operating around 488  nm by intracavity second-harmonic generation. By using lithium triborate crystal, we have achieved over 1.3  W continuous wave blue-green power at 488  nm with a 5  nm tunability


Tunable high-power high-brightness linearly polarized vertical external cavity surface emitting lasers
L. Fan, M. Fallahi, J.T. Murray, R. Bedford, Y. Kaneda, A.R. Zakharian, J. Hader, J.V. Moloney, W. Stolz, S.W. Koch, Appl. Phys. Lett. 88 (2006) 021105
We report on the development and the demonstration of tunable high-power high-brightness linearly polarized vertical-external-cavity surface-emitting lasers (VECSELs). A V-shaped cavity, in which the antireflection-coated VECSEL chip (active mirror) is located at the fold, and a birefringent filter are employed to achieve a large wavelength tuning range. Multiwatt cw linearly polarized TEM00 output with a 20  nm tuning range and narrow linewidth is demonstrated at room temperature.


Over 3 W high-efficiency vertical-external-cavity-surface-emitting lasers and application as efficient fiber laser pump sources
L. Fan, M.Fallahi, J. Hader, A.R. Zakharian, M. Kolesik, J.V. Moloney, T. Qiu, A. Schulzgen, N. Peyghambarian W. Stolz, S.W. Koch, J.T. Murray, Appl. Phys. Lett. 86 (2005) 211116
We report on the design and fabrication of high-power, high-brightness diode-pumped vertical-external-cavity surface-emitting lasers. Over 3 W continuous wave fundamental transverse mode (TEM00) output at 980 nm with a high slope efficiency of 44% is demonstrated at room temperature. The diffraction-limited beam with M2 factor of 1.15 at high-power operation is achieved. A vertical-external-cavity surface-emitting laser operating near 976 nm with a diffraction-limited beam is used to pump the core of 3 cm long Er/Yb-codoped single-mode phosphate fiber lasers. An output power in excess of 250 mW at 1535 nm with a slope efficiency of 29% is obtained without any cooling.


High-power optically pumped VECSEL using a double-well resonant periodic gain structure
L. Fan, K. Hader, M. Schillgalies, M. Fallahi, A.R. Zakharian, J.V. Moloney, R. Bedford, J.T. Murray, S.W. Koch, W. Stolz, IEEE Photon. Technol. Lett. 17 (2005) 1764


Low threshold 1260 nm (GaIn) (NAs) semiconductor disk laser
W. Diehl, P. Brick, B. Kunert, S. Reinhard, K. Volz, W. Stolz, Appl. Phys. Lett. 91 (2007) 071103
Low threshold cw laser emission from a semiconductor disk laser emitting at 1260 nm was demonstrated. Using high quality metal-organic vapor phase epitaxy (GaIn) (NAs) material, nonradiative processes could be minimized. As a consequence, threshold pump power densities have been reduced down to 5 kW/cm(2). The capture efficiency of carriers into the quantum wells was found to be uncritical.


5-W Yellow Laser by Intracavity Frequency Doubling of High-Power Vertical-External-Cavity Surface-Emitting Laser
M. Fallahi, L. Fan, Y. Kaneda, C. Hessenius, J. Hader, H. Li, J.V. Moloney, B. Kunert, W. Stolz, S.W. Koch, J. Murray, R. Bedford, Photonic Technology Letters, IEEE, Vol. 20, Issue 20 (2008) 1700-1702
We report on the development of a high-power tunable yellow–orange laser. It is based on intracavity frequency doubling of a widely tunable, highly strained InGaAs–GaAs vertical-external-cavity surface-emitting laser operating near 1175 nm. Over 5 W of continuous-wave output power is achieved and is tunable over a 15-nm band centered at 587 nm. This compact low-cost high-power yellow–orange laser provides an innovative alternative for sodium guidestar lasers, medical and communication applications.

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