Optimization of GaAsP/AlGaAs-based QW laser structures for high power 800 nm operation

We present a detailed study of the MOVPE growth of 800 nm diode laser structures based on the combination of a GaAsP quantum well with well-established AlGaAs waveguide structures. By optimizing the strain and thickness of the quantum well highly-reliable diode lasers with low threshold current and high efficiency were demonstrated. 100 μm aperture “broad area” devices mounted epi-side up achieve a CW output power of 8.9 W with a wall-plug efficiency of 50%. These output powers represent record values for diode lasers in this wavelength range. Reliability measurements at 1.5 W and 50°C ambient temperature suggest lifetimes >10 000 h.     

MOVPE growth of AlGaAs/GaInP diode lasers

GaAs-based diode lasers for emission wavelengths between 800 nm and 1060 nm with AlGaAs-cladding and GaInP-waveguide layers were grown by MOVPE. For wavelengths above 940 nm broad area devices with InGaAs QWs show state-of-the-art threshold current densities. Ridge-waveguide lasers fabricated by selective etching achieve 200 mW CW monomode output powers. (In)GaAsP QW-based diode lasers with an emitting wavelengths around 800 nm suffer from problems at the upper GaInP/AlGaAs interface. Asymmetric structures with a lower AlGaAs/GaInP and an upper AlGaAs/AlGaAs waveguide not only avoid this interface but also offer better carrier confinement. Such structures show very high slope efficiencies and a high T₀. Maximum output powers of 7 W CW are obtained from 4 mm long devices.     

Interdiffusion and relaxation in metalorganic vapor phase epitaxy grown InGaAs/GaAs strained layer quantum wells

Low pressure metalorganic vapor phase epitaxy grown strained InGaAs/GaAs quantum well structures have been characterized by photoluminescence and x-ray diffraction. It is shown that beyond the pseudomorphic limit, these structures show considerable gallium/indium interdiffusion at the interfaces and partial strain relaxation in the quantum well layers.     

Influence of oxygen in AlGaAs-based laser structures with Al-Free active region on device properties

AlGaAs-based lasers with GaAsP active regions for emission wavelengths near 730 nm and 800 nm were studied. Trimethyl aluminum sources with different levels of oxygen concentration were used for the deposition of the laser structures. The laser data show that the oxygen level in the AlGaAs wave guides is very critical for the performance of the 730 nm devices, even for the use of an Al-free active region, while its influence is weak for the 800 nm devices. Using the TMAl source leading to the lowest O-uptake in the AlGaAs wave guides from such structures, 7 W output power and a degradation rate of 1 10⁻⁵h⁻¹ at 2 W cw (100 μm stripe width × 4 mm, 25°C, 2000 h) are achieved for 730 nm emission.     

Structural properties of ZnSy Se1−yZnSe/GaAs (001) heterostructures grown by photoassisted metalorganic vapor phase epitaxy

ZnS_ySe_1−yZnSe/GaAs (001) heterostructures have been grown by photoassisted metalorganic vapor phase epitaxy, using the sources dimethylzinc, dimethylselenium, diethylsulfur, and irradiation by a Hg arc lamp. The solid phase composition vs gas phase composition characteristics have been determined for ZnSy_ySe_1−y grown with different mole fractions of dimethylselenium and different temperatures. Although the growth is not mass-transport controlled with respect to the column VI precursors, the solid phase composition vs gas phase composition characteristics are sufficiently gradual so that good compositional control and lattice matching to GaAs substrates can be readily achieved by photoassisted growth in the temperature range 360°C ≤ T ≤ 400°C. ZnSe/GaAs (001) single heterostructures were grown by a two-step process with ZnSe thicknesses in the range from 54 nm to 776 nm. Based on 004 x-ray rocking curve full width at half maximums (FWHMs), we have determined that the critical layer thickness is h_c ≤200 nm. Using the classical method involving strain, lattice relaxation is undetectable in layers thinner than 270 nm for the growth conditions used here. Therefore, the rocking curve FWHM is a more sensitive indicator of lattice relaxation than the residual strain. For ZnS_ySe_1−y layers grown on ZnSe buffers at 400°C, the measured dislocation density-thickness product Dh increases monotonically with the room temperature mismatch. Lower values of the Dh product are obtained for epitaxy on 135 nm buffers compared to the case of 270 nm buffers. This difference is due to the fact that the 135 nm ZnSe buffers are pseudomorphic as deposited. For ZnS_ySe_1−y layers grown on 135 nm ZnSe buffers at 360°C, the minimum dislocation density corresponds approximately to room-temperature lattice matching (y ∼ 5.9%), rather than growth temperature lattice matching (y ∼ 7.6%). Epitaxial layers with lower dislocation densities demonstrated superior optical quality, as judged by the near-band edge/deep level emission peak intensity ratio and the near band edge absolute peak intensity from 300K photoluminescence measurements.     

Metalorganic vapor phase epitaxial growth of GaInAsP/GaAs

Ga_xAs_yP_1−y lattice matched to GaAs has been grown by low pressure metalorganic phase vapor epitaxy over the entire compositional range. At T_G = 670°C broad peaks of low intensity are observed in the 10K photoluminescence for y = 0.2–0.4 due to the predicted miscibility gap in this compositional region. An increase in growth temperature leads to a smaller miscibility gap. The band gap as well as the morphology show a strong dependence on substrate misorientation. The smoothest GalnAsP surfaces are obtained on exact oriented substrates. For the ternary GalnP the surface roughness is correlated to the degree of ordering in the temperature range of 600 to 750°C. The smallest band gap together with the smoothest surface is obtained on (100) 2° off to (111)B. Ordering effects are also observed in the quaternary GalnAsP. Broad-area lasers processed from the grown layers show high slope efficiency (0.9 W/A) and low internal losses (<3 cm⁻¹).     

MOVPE growth of strained InGaAs/lnAIAs MQWs for a polarization-insensitive electroabsorption modulator

Metalorganic vapor phase epitaxial growth of a strained InGaAs/lnAIAs multiquantum well (MQW) structure was carried out for optical electroabsorption modulators. A high-quality MQW layer can be grown by introducing compressive strain into InAlAs barrier layers against tensile-strained well layers. We have also demonstrated strained InGaAs/lnAIAs MQW electroabsorption modulators with polarization insensitivity by using these layers and have obtained a highquality modulator with a low driving voltage of 1.7 V and a wide 3-dB bandwidth of over 20 GHz.     

Effect of temperature on InGaAsP alloy composition

The influence of growth temperature on the composition of InGaAsP films grown by low pressure metalorganic vapor phase epitaxy (MOVPE) is reported for quaternary (Q) alloys having bandgap wavelengths of λ_g = 1.1, 1.3, and 1.5 μn. Films with these different Q-compositions were deposited lattice matched to InP at a growth temperature of 675°C. Subsequent growth experiments were then performed for each Q-composition in which the input gas flow rates were kept the same and only the temperature changed in 25°C decrements down to 600°C. Photoluminescence (PL) and lattice mismatch (LMM) measurements of the resulting films were used to determine the effect of growth temperature on film composition. The PL data indicate a temperature shift in the PL wavelength of −1.8 nm/ °C for the 1.5Q composition, −2.9 nm/°C for 1.3Q, and −4.3 nm/°C for 1.1Q. Negative shifts were also observed in LMM of −80 ppm/°C for 1.5Q, −150 ppm/°C for 1.3Q, and −250 ppm/°C for 1.1Q. The Ga/In and P/As ratios of the Q-filmswere measured by secondary ion mass spectroscopy and correlated with full-wafer maps of the PL wavelength and lattice mismatch to gain insight into the processes responsible for wafer nonuniformity in MOVPE.     

MOVPE growth of InPSb/InAs heterostructures for mid-infrared emitters

We investigated the growth of InPSb on GaSb or InAs by low pressure (20 mbar) metalorganic vapor phase epitaxy (MOVPE). Trimethylindium, triethylantimony, and phosphine were used as starting materials. High resolution x-ray diffraction, photoluminescence at 10K, Hall measurements at 300 and 77K as well as scanning electron microscopy and scanning tunneling electron microscopy investigations were carried out to verify the layer properties. Lattice-matched InPSb layers on InAs substrate grown at 520°C show mirror-like surfaces and sharp x-ray peaks. N-type doping of InP_0.69Sb_0.31 was carried out with H₂S and p-type doping was achieved with DEZn. Maximum electron concentrations of 2×10¹⁹ cm⁻³ and hole concentrations exceeding 10¹⁸ cm⁻³ were obtained after annealing in N₂ ambient. The thermal stability of InPSb was studied during annealing experiments carried out at 500°C up to 30 min. The compositional integrity of the lattice proves to be stable and the InAs/InPSb interface can be improved. Multiple quantum well structures, pn-junction diodes and the two-dimensional electron gas at the InPSb/InAs/InPSb quantum wells were investigated to demonstrate the properties of the material.     

A1.3 μm strained quantum well laser on a graded InGaAs buffer with a GaAs substrate

We grew a 1.3 μm strained-layer quantum well (SL-QW) laser with InGaP cladding layers on a lattice-relaxation buffer layer by metalorganic vapor phase epitaxy. For the lattice-relaxation buffer, we used a compositionally graded InGaAs/GaAs structure. The significantly reduced surface roughness of the InGaP cladding layers achieved by supplying a large amount of H₂Se enables CW operation of our 1.3 μm SL-QW laser. We achieved a low threshold current of less than 10 mA and a high characteristic temperature of 100K around room temperature.     

Investigation of strain-compensated lnGaAs(P)/lnGaAs(P)/lnP multiple quantum well structures grown by LP-MOVPE

A controversy exists regarding the effectiveness, in the high strain case, of the strain-compensated InGaAs(P)/InGaAs(P)/InP multiple quantum well (MQW) structures. In this paper, the mechanism of the crystal quality degradation in the high strain case is analyzed. Based on our experiments and analysis, we suggest that the crystal quality degradation is predominately affected by the growth temperature and V/III ratios in the gas phase. We demonstrate that, in the case of high strain in the wells, high quality and stable strain-compensated MQW structures can be grown at relatively low growth temperature and relatively high V/III ratios in the gas phase through decreasing the strain in barriers and increasing the thicknesses of barriers simultaneously to achieve zero net strain.     

The role of surface adsorbates in the metalorganic vapor phase epitaxial growth of (Hg,Cd)Te onto (100) GaAs Substrates

It has been established that a compound present as an impurity in the propan-2-ol used in the preparation of GaAs (100) substrates for the metalorganic vapor phase epitaxy growth of (Hg,Cd)Te has a marked effect on the crystalline perfection and surface morphology of the resulting layers. In particular, the presence of this species, which contains Na, ensures that (i) the epitaxial overgrowth is of (100) orientation without the need for ZnTe nucleation layers, and (ii) the density of pyramidal hillocks on the surface can be reproducibly < 10 cm⁻².     

The effects of laser irradiation on InGaAs/GaAs multiple quantum wells grown by metalorganic molecular beam epitaxy

We studied the effects of Ar ion laser irradiation during the growth of InGaAs/ GaAs multiple quantum wells (MQW) structures by metalorganic molecular beam epitaxy. Structural and optical properties were characterized by Nomarski microscopy, Dektak stylus profiler, and low-temperature photoluminescence (PL) measurements. For MQW structures grown at a relatively low substrate temperature (500°C), the laser irradiation influences greatly the growth process of the In^Ga^^As well and results in a large blue shift of about 2000à in the PL peak. Such a large blue shift suggests that laser modification during growth could have some novel applications in optoelectronics. On the other hand, the laser irradiation has relatively small effects on samples grown at a higher substrate temperature (550°C).     

Impact of growth rate on the quality of ZNS-MQW InGaAsP/InP laser structures grown by LP-MOVPE

We investigated the influence of the growth rate on the quality of zero-net-strained InGaAsP/InGaAsP/InP multiquantum well structures for 1.55 μm emission grown by low pressure metalorganic vapor phase epitaxy. The samples consisted of fixed compressive strained wells (ɛ=+1%) and tensile strained barriers (ɛ=−0.5%) grown with different quaternary bandgap wavelengths (λ_B=1.1–1.4 μm). Using higher growth rates, we obtained for the first time high quality zero net strained multi quantum well structures, regardless having constant group V composition in the well and barriers. The samples were analyzed by x-ray diffraction, photoluminescence and atomic force microscopy techniques. The amplitude of surface modulation roughness along [011] direction decreased from 20 nm to 0.53 nm with increasing growth rate and/or quaternary compositions grown outside the miscibility gap. A new deep PL broad emission band strongly correlated with the onset of wavy layer growth is also reported. Broad area and ridge waveguide lasers with 10 wells exhibited low losses (34 cm⁻¹) and low threshold current densities at infinite cavity length (1020 A·cm⁻² and 1190 A·cm⁻², respectively).     

In0.2Ga0.8As/GaAs quantum well laser with C doped cladding and ohmic contact layers

Carbon doping in Al_xGa_1−xAs was achieved using different approaches. The moderate growth temperature of 650°C was employed to grow C bulk-doped Al_xGa_1−xAs with a high Al mole fraction. The hole-density was altered using different V/III ratios. The trimethylaluminum (TMAl) was used as an effective C δ-doping precursor for growth of C δ-doped pipi doping superlattices in Al_xGa_1−xAs. the average hole-density of C δ-doped pipi superlattices was greater than 2−3 × 10¹⁹ cm⁻³. Zn-free GRINSCH In_0.2Ga_0.8As/GaAs laser structures were then grown using the C bulk-doped Al_xGa_1−xAs and C δ-doped pipi superlattice as a cladding and ohmic contact layer, respectively. The ridge waveguide laser diodes were fabricated and characterized to verify flexibility of these two doping approaches for device structures.     

Self-organization phenomenon of strained InGaAs on InP (311) substrates grown by metalorganic vapor phase epitaxy

We have demonstrated that a self-organization phenomenon occurs in strained InGaAs system on InP (311) substrates grown by metalorganic vapor phase epitaxy. This suggests that a similar formation process of nanocrystals exists not only on the GaAs (311)B substrate but also on the InP (311)B substrate. However, the ordering and the size homogeneity of the self-organized nanocrystals are slightly worse than those of the InGaAs/AlGaAs system on the GaAs (311)B substrate. The tensilely strained condition of a InGaAs/InP system with growth interruption in a PH₃ atmosphere reveals a surface morphology with nanocrystals even on the InP (100) substrate. It was found that strain energy and high growth temperature are important factors for self-organization on III-V compound semiconductors. Preliminary results indicate that the self-organized nanostructures in strained InGaAs/InP systems on InP substrates exhibit room temperature photoluminescent emissions at a wavelength of around 1.3 p.m.     

MOVPE production reactors for high temperature electronics

For the fabrication of epitaxial films of silicon carbide or the Group III nitrides, high growth temperatures (up to 1700°C) and fast heating and cooling of the growth environment have been found to be necessary. A range of production systems meeting these requirements has been designed with different loading capacities. In this paper, we present results from various machines showing the high quality and excellent homogeneity obtainable for 3C-SiC on Si and on 6H-SiC, as well as GaN on sapphire.     

Minimally cooled heterojunction laser heterodyne detectors in metalorganic vapor phase epitaxially grown Hg1-xCdxTe

By taking advantage of Auger suppression techniques, the leakage currents of room temperature infrared detectors operating in the LWIR band can be greatly reduced. At present, these detectors suffer from large 1/f noise and hence the improvement in the detectivity resulting from the reduced leakage currents can only be realized at high frequencies. However, this is not a problem for heterodyne systems which employ intermediate frequencies above 40 MHz. A thermo-electrically cooled Auger suppressed infrared detector operated at 260K has been studied as a heterodyne detector. The device was operated with the application of sufficient local oscillator power to double its dark current (about 0.3 mW) and a NEP of 2 x 10^-19 W Hz⁻¹ was deduced from heterodyne measurements. The frequency response is presently limited by a combination of the detector capacitance and the series resistance to about 70 MHz and ways to reduce this series resistance are considered.     

Role of GaAs bounding layers in improving OMVPE growth and performance of strained-layer inGaAs/AIGaAs quantum-well diode lasers

In the growth of organometallic vapor phase epitaxy of InGaAs/AIGaAs single-quan-tum-well heterostructures for strained-layer diode lasers, the growth temperature is 100 to 200° C lower for the InGaAs quantum-well layer than for the AlGaAs cladding layers. Earlier studies showed that laser performance is greatly improved by sandwiching the InGaAs layer between lower and upper GaAs bounding layers that are grown during the times before and after InGaAs growth when the substrate temperature is decreased and increased, respectively. In this investigation, it has been found that laser performance is influenced mainly by the upper bounding layer rather than the lower one. By using Auger analysis in combination with Ar-ion sputtering to determine the composition depth profile of In_0.2Ga_0.8As/GaAs test structures layer without AlGaAs layers, it has been shown that the role of the upper bounding layer is to prevent the evaporation of In from the InGaAs quantum-well layer during the interval before the deposition of the upper AlGaAs cladding layer.     

Metalorganic vapor phase epitaxial growth and structural characterization of GaAs/InP heterostructures

Highly mismatched GaAs epitaxial layers with thickness ranging from 15 nm to 7 μm have been grown on InP substrates by atomospheric pressure metalorganic vapor phase epitaxy. Layers thinner than 30 nm exhibited 3-D growth mechanism; in the thicker layers, the islands coalesced and then the growth followed the layer by layer mechanism. The elastic strain and the extended defects have been studied by high resolution x-ray diffraction and transmission electron microscopy, respectively. The common observation of planar defects, misfit, and threading dislocations in the layers has been confirmed. The results on the elastic strain release have been discussed on the basis of the equilibrium theory.