Group-V composition control for InGaAsP grown by gas source molecular beam epitaxy

Based on our kinetics models for gas source molecular beam epitaxy of mixed group-V ternary materials, the group-V composition control in In_yGa_1−yAs_1−xP_x epilayers has been studied. The P or As composition in In_yGa_1−yAs_1−xP_x (lattice matched to InP or GaAs) can be obtained from a simple equation for substrate temperatures below 500°C. This has been verified by a series of experimental results.     

A novel pseudomorphic (GaAs1−xSbx-InyGa1−yAs)/GaAs bilayer-quantum-well structure lattice-matched to GaAs for long-wavelength optoelectronics

Two types of quantum well (QW) structures grown lattice matched on (100) GaAs have been studied. The first type of structure consists of pseudomorphic GaAs_xSb_1-x/GaAs (x≤0.3) SQWs which show emission wavelengths longer than those reported for pseudomorphic In_yGa_1−yAs/GaAs QWs. However, the attractive emission wavelength of 1.3 μm has not been achieved. To reach this goal, a novel type of bilayer QW (BQW) has been grown consisting of a stack of two adjacent pseudomorphic layers of GaAs_xSb_1−x and In Ga_1-y As embedded between GaAs confinement layers. In this BQW, a type-II heterojunction is formed between GaAs_xSb_1−x and In_yGa_1−yAs, resulting in a spatially indirect radiative recombination of electrons and holes at emission wavelengths longer than those achieved in the GaAs_xSb_1−x/GaAs and Ii_yGa_1−yAs/GaAs SQWs. The longest 300K emission wavelength observed so far was 1.332 μm.     

Bandgap and lattice constant of GaInAsP as a function of alloy composition

Published data for the composition dependence of the room-temperature bandgap (E_g) and lattice constant (a_o) in the pseudobinary Ga_yIn_1-yAs, Ga_yIn_1-yP, GaAs_xP_l-x, and InAs_xP_l-x systems have been used to derive the following equations for the quaternary Ga_yIn_l-yAs_x P_l-x, alloys: $$\begin{gathered} a_o ({\AA}) = 5.87 + 0.18x - 0.42y + 0.02xy \hfill \\ E_g (eV) = 1.35 - x + 1.4y - 0.33xy - (0.758 - 0.28x)y(1 - y) \hfill \\ - (0.101 + 0.109y) x(1 - x). \hfill \\ \end{gathered} $$ Available experimental data are in excellent agreement with these equations.     

The effect of trimethylaluminum concentration on the incorporation of P In AlxGa1−xPyAs1−y grown by organometallic vapor phase epitaxy

The organometallic vapor phase epitaxial (OM-VPE) growth of Al_xGa_1-xP_yAs_1-y on graded GaP_yAs_1-yGaAs in the compositional range 0 < x < 0.9 and 0 < y < 0.6 is reported. It is found that composition control can be easily achieved, and that the vapor phase ratio of trimethylaluminum to trimethylgallium strongly influences the incorporation of P in the solid. A model is developed which explains this in terms of competing reaction rates. The model gives a good fit to the experimental data.     

Liquid phase epitaxial growth of Gal-xInxSb on GaSb by stepwise grading

The Ga_l-xIn_xSb alloy system is a potentially important material for the fabrication of middle wavelength infrared detectors and emitters. In order to develop the use of this material we have investigated the liquid phase epitaxial growth of Ga_1−xIn_xSb on GaSb via stepwise grading in the range of 400–600°C using a horizontal slider boat in a transparent furnace. Single crystal layers of Ga_1−xIn_xSb have been obtained for the composition range 0<x<.30. As-grown undoped layers are p-type and have been characterized by lattice constant, surface morphology, bandgap, carrier concentration and carrier lifetime.     

Liquid phase epitaxial growth of InAsxSbyPl-x-y layers on InAs

High quality InAs_xSb_yP_l-x-y quaternary layers, which are lattice matched to InAs, have been grown successfully on InAs substrates by liquid phase epitaxy. Both Graded and constant composition InAs_xSb_yP_l-x-y layers have been grown. In addition, the graded InAs_xSb_yP_l-x-y layer has been used as a buffer layer for the growth of InAs_l-xSb_x on an InAs substrate. Research supported in part by Commander, U. S. Army Missile Command, Attn: AMSMI-RNS, Redstone Arsenal, AL 35809 and ARPA-Advanced Research Projects Agency, 1400 Wilson Boulevard, Arlington, VA 22209.     

Measured compositions and laser emission wavelengths of GaXIn1−XAsyP1−y lpe layers lattice-matched TO InP Substrates

The alloy compositions of Ga_XIn_1−XAs_yP_1−y LPE layers lattice-matched to InP substrates have been determined by electron microprobe analysis. The composition data are well repre-sented by x = 0.40y + 0.067y². The emission wavelengths of lattice-matched Ga_XIn_1−XAs_yP_1−y/InP double-heterostructure diode lasers have been measured at 300 and 80 K. The photon energies for laser emission at 300 K are given by hΝ(eV) = 1.307 − 0. 60y + 0.03y². The emission energies at 80 K are 57 meV higher. This work was sponsored by the Department of the Air Force.     

Low pressure metalorganic chemical vapor deposition of InP and related compounds

The low pressure metalorganic chemical vapor deposition epitaxial growth and characterization of InP, Ga_0.47In_0.53 As and Ga_xIn_1-xAs_yP_1-y, lattice-matched to InP substrate are described. The layers were found to have the same etch pit density (EPD) as the substrate. The best mobility obtained for InP was 5300 cm² V⁻¹S⁻¹ at 300 K and 58 900 cm² V⁻¹ S⁻¹ at 77₂K, and for GaInAs was 11900 cm² V⁻¹ S⁻¹ at 300 K, 54 600 cm² V⁻¹ S⁻¹ at 77 K and 90 000 cm V⁻¹S⁻¹ at 2°K. We report the first successful growth of a GaInAs-InP superlattice and the enhanced mobility of a two dimensional electron gas at a GaInAs -InP heterojunction grown by LP-MO CVD. LP MO CVD material has been used for GaInAsPInP, DH lasers emitting at 1.3 um and 1.5 um. These devices exhibit a low threshold current, a slightly higher than liquid phase epitaxy devices and a high differential quantum efficiency of 60%. Fundamental transverse mode oscillation has been achieved up to a power outpout of 10 mW. Threshold currents as low as 200 mA dc have been measured for devices with a stripe width of 9 um and a cavity length of 300 um for emission at 1.5 um. Values of T in the range 64–80 C have been obtained. Preliminary life testing has been carried out at room temperature on a few laser diodes (λ = 1.5μm). Operation at constant current for severalthousand hours has been achieved with no change in the threshold current.     

Nickel silicidation techniques for strained Si1?xGex, Si1?x?yGexCy, and Si1?yCy alloys material-device applications

A nickel silicide process for Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy materials compatible with Si technology has been developed. Low-resistivity-phase (12–20 μΘ cm) nickel silicides have been obtained for these alloys with different low sheet-resistance temperature windows. The study shows that thin (15–18 nm) silicide layers with high crystalline quality, smooth silicide surface, and smooth interface between silicide and the underlying material are achievable. The technique could be used to combine the benefits of Ni silicide and Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloys. The technique is promising for Si or Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy-based metal-oxide semiconductor, field-effect transistors (MOSFETs) or other device applications.     

Effect of surface encapsulation and As4 overpressure on Si diffusion and impurity-induced layer disordering in GaAs,AlxGa1-xAs,and AlxGa1-xAs-GaAs quantum well heterostructures

Data are presented demonstrating that the surface encapsulant and the As₄ overpressure strongly affect Si diffusion in GaAs and Al_xGa_1-xAs, and thus are important parameters in impurity-induced layer disordering. Increasing As₄ overpressure results in anincrease in diffusion depth in the case of GaAs, and adecrease in diffusion depth for Al_xGa_1-xAs. In addition, the band-edge exciton is observed in absorption on an Al_xGa_1-xAs-GaAs superlattice that is diffused with Si and is converted to bulk crystal Al_yGa_1-yAs via impurity-induced layer disordering. In contrast, the exciton is not observed in absorption on GaAs diffused with Si in spite of the high degree of compensation. These data indicate that the Si diffusion process, and the properties of the diffused material, are different for GaAs and for Al_xGa_1-xAs-GaAs superlattices converted into uniform Al_yGa_1-yAs (0 ≤y ≤x ≤ 1) via impurity-induced layer disordering with the amphoteric dopant Si.     

Efficient 2.0–2.6 μm wavelength photoluminescence from narrow bandgap InAsP/InGaAs double heterostructures grown on InP substrates

Photoluminescence spectra and efficiency have been measured for several strained InAs_yP_1−yIn_xGa_1−xAs (0.28 < y ≤ 0.62; 0.66 ≤ x ≤ 0.83) double heterostructures grown by vapor phase epitaxy on InP substrates with graded InAsP buffer layers. Luminescence peak positions between the wavelengths of 1.99 and 2.57 (μm at a temperature of 295K are consistent with bandgap luminescence from the In_xGa_1−xAs active regions. Despite a high density of dislocations in the buffer layers, internal radiative recombination efficiencies of from 25 to 50% for the structures are found at 295K.     

Vapor-grown In1−xGaxP electroluminescent junctions on GaAs

In_1?xGa_xP vapor-grown electroluminescent junctions have been deposited directly onto GaAs substrates. For these layers, an alloy composition within a few mole percent of the lattice-matching composition of 51.5 mole percent GaP has been found to be essential for high luminous efficiencies and for the avoidance of microcracks throughout the epitaxial layer. For In_1?xGa_xP alloys near this composition, the electroluminescence characteristics of the diodes have been found to be excellent, with room-temperature external quantum efficiencies as high as 0.2% attained for red emission near 6600 Å. The properties of In_.5Ga_.5P junction structures deposited directly onto GaAs ar? compared with those of In_1?xGa_xP layers previously prepared on GaP substrates.     

Engineering phase formation thermo-chemistry for crystal growth of homogeneous ternary and quaternary III–V compound semiconductors from melts

Based on intrinsic alloy phase formation chemistry and thermodynamics, a novel and unique way of producing compositionally homogeneous multi-component (binary, ternary, quaternary) semiconductor materials is presented. A free energy minimization computer program licensed from AEA Technology Engineering Software, Inc., has been employed to study the composition of the solidifying phases from Ga-In-As-Sb melts at different temperatures and with various liquid compositions. The solid phases have been identified (theoretically and experimentally) to be either ternary compounds of Ga_1−xIn_xAs_ySb_1−y depending on the melt temperature and composition. By engineering the thermochemistry of preferential phase formation in the Ga-In-As-Sb melt, compositionally uniform, single phase, crack free, large polycrystalline Ga_1−xIn_xSb and Ga_1−xIn_xAs have been grown.     

A comparison of TMG with TEG for the growth of InxGa1−xAs

MOCVD growth of In_xGa_1?xAs from trimethylgallium (TMG), triethylgallium (TEG), trimethylindium (TMI) and arsine was studied over a wide range of growth conditions. It was found that the In_xGa_1?xAs strain with respect to InP is strongly influenced by the arsine concentration when grown with TEG and TMI. In contrast the In_xGa_1?xAs strain was independent of arsine concentration when grown with TMG and TMI. It was also observed that the growth rate of In_xGa_1?xAs is higher for TMG than for TEG with the same TMI and arsine flow. In addition an interaction between TEG and dimethylzinc (DMZ) was also observed. We show that MOCVD growth process involves many complex reactions and cannot be considered as a simple decomposition of each precursor. The interactions between precursors, which takes place in the gas phase or on the growing surface, has to be considered. We have utilized the TEG/arsine interaction for the growth of strain compensated superlattices by modulating the arsine flow into the reactor chamber while keeping the TEG and TMI constant. Structures with up to 100 periods of 100 Å of +1% In_0.6Ga_0.4As and 200 Å of ?0.5% In_0.5Ga_0.5As were grown with excellent characteristics.     

Visible light-emitting diodes grown on optimized ∇x[InxGa1−x]P/GaP epitaxial transparent substrates with controlled dislocation density

Epitaxial transparent-substrate light-emitting diodes (ETS-LEDs) have been fabricated on optimized graded buffers of In_xGa_1−xP on GaP (∇_x[In_xGa_1−x]P/GaP) that feature controlled threading dislocation densities of 3×10⁶ cm⁻². The ETSLEDs show increasing efficiency from 575 nm to 655 nm, in marked contrast to previous reports where performance drops above 600 nm, and feature the lowest spectral widths ever reported in ∇_x[In_xGa_1−x]P/GaP. The improvement over earlier reports is attributed to large mean dislocation spacings in optimized ∇_x[In_xGa_1−x]P/GaP, which are an order of magnitude greater than the mean carrier diffusion length. A slight performance decline remains at 655 nm, but the overall performance of this first generation of ETS-LEDs is promising.     

Formation mechanism of InxGa1−xAs ohmic contacts to n-type GaAs prepared by radio frequency sputtering

The formation mechanisms of InAs/Ni/W ohmic contacts to n-type GaAs prepared by radio-frequency (rf) sputtering were studied by measuring contact resistances (R_c) using a transmission line method and by analyzing the interfacial structure mainly by x-ray diffraction and transmission electron microscopy. Current-voltage characteristics of the InAs/Ni/W contacts after annealing at temperatures above 600°C showed “ohmic-like behavior.” In order to obtain the “ohmic” behavior in the contacts, pre-heating at 300°C prior to high temperature annealing was found to be essential. The contacts showed ohmic behavior after annealing at temperatures in the range of 500∼850°C and contact resistance values of as low as ∼0.3Ω-mm were obtained. By analyzing the interfacial structures of these contacts, In_xGa_1−xAs layers with low density of misfit dislocations at the In_xGa_1−xAs and GaAs interface were observed to grow epitaxially on the GaAs substrate upon heating at high temperatures. This intermediate In_xGa_1−xAs layer is believed to divide the high energy barrier at the contact metal and GaAs interface into two low barriers, resulting in reduction of the contact resistance. In addition, Ni was found to play a key role to relax a strain in the In_xGa_1−xAs layer (introduced due to lattice mismatch between the In_xGa_1−xAs and GaAs) by forming an intermediate Ni_xGaAs layer on the GaAs surface prior to formation of the In_xGa_1−xxAs layer.     

Spinodal decomposition and clustering in III/V alloys

The criteria for clustering and spinodal decomposition in III/V pseudobinary and quaternary solid alloys are examined. A chemical driving force for clustering and phase separation exists in some ternary and most quaternary alloys. However, single crystalline alloys are shown to be stabilized by the coherency strain energy inherent in any clustering or spinodal decomposition in alloys where lattice parameter is a function of composition. Analytical expressions are derived for T_s, the temperature above which no clustering or phase separation should occur. Most III/V pseudobinary and quaternary alloys are stable at all temperatures. Numerical techniques are used to calculate spinodal isotherms. Results are presented for the systems Ga_xIn_1−x As P_1−y, A1_xGa_1−xAs_ySb_1−y, and Ga_xIn_1−x As P_1−y. This work was supported by the Department of Energy, contract No. DE-AT 03-81 ER 10934.     

Photoluminescence of Ga1−x InxAsySb1−y solid solutions lattice-matched to InAs

Photoluminescence of Ga_1?x In _x As _y Sb_1?y (0.08<x<0.22) epilayers lattice-matched to InAs substrate was investigated for the first time at 80 K, and the band gap of solid solutions was evaluated experimentally. It was demonstrated that the intensity of the band-to-band radiative recombination for p-GaInAsSb undoped layers depends on the composition of the quaternary solid solution and is governed by the concentration of intrinsic structural defects. For an n-GaInAsSb:Te donor-doped layer, the band-to-band recombination band and an additional emission band were observed. The latter band is related to the radiative recombination via the deep acceptor level formed by an intrinsic complex V _GaTe with the activation energy E _DA =122 meV.     

Development of InxGa1−xAs-based ohmic contacts for p-type GaAs by radio-frequency sputtering

In_xGa_1−xAs-based ohmic contacts which showed excellent contact properties for n-GaAs were demonstrated to be applicable to p-GaAs ohmic contacts. These contacts, prepared by radio-frequency sputtering, provided low contact resistance (0.2 Ω-mm), excellent thermal stability, smooth surface, and good reproducibility. The contact resistances had a weak dependence on the annealing temperatures, which was desirable in a manufacturing view point. This weak temperature dependence was explained to be due to a unique Schottky barrier height at the metal/p-In_xGa_1−xAs interface which does not depend on the In concentration in the In_xGa_1−xAs layer. The present experiment showed the possibility of simultaneous preparation of ohmic contacts for both n and p-GaAs using the same contact materials.     

Properties and use of ln0.5(AlxGa1-x)0.5P and AlxGa1-x as native oxides in heterostructure lasers

Data are presented demonstrating the formation of native oxides from high Al composition In_0.5(Al_xGa_1-x)_0.5P (x≳ 0.9) by simple annealing in a “wet” ambient. The oxidation occurs by reaction of the high Al composition crystal with H₂O vapor (in a N₂ carrier gas) at elevated temperatures (≥500° C) and results in stable transparent oxides. Secondary ion mass spectrometry (SIMS) as well as scanning and transmission electron microscopy (SEM and TEM) are employed to evaluate the oxide properties, composition, and oxide-semiconductor interface. The properties of native oxides of the In_0.5(Al_xGa_1-x)_0.5P system are compared to those of the Al_xGa_1-xAs system. Possible reaction mechanisms and oxidation kinetics are considered. The In_0.5(Al_xGa_1-x)_0.5P native oxide is shown to be of sufficient quality to be employed in the fabrication of stripe-geometry In_0.5(Al_xGa_1-x)_0.5P visible-spectrum laser diodes.