The preparation of modulation-doped GaAs/GaAs1-xPx strained-layer superlattices by metal organic chemical vapor deposition

Modulation-doped and uniformly doped GaAs/GaAs_1-xP_x strained-layer superlattices (SLS’s) have been prepared by metal organic chemical vapor deposition in a vertical, atmospheric pressure, quartz reaction chamber. The layers were doped with Se or Si by using a H₂Se or SiH₄ source and by using a vent-run valve-configuration to minimize dopant tailing. Carrier concentrations and mobilities were determined from Hall measurements at 300 and 77 K. The Se modulation-doped SLS’s with carrier concentrations in the range of 10¹⁶ to 10¹⁸ cm^-13 exhibited enhanced transport properties when compared to the properties of epitaxial GaAs prepared under the same conditions. The use of molecular sieves to purify the arsine or the use of SiH₄ resulted in lower mobilities for the SLS’s and the epitaxial GaAs layers. The presence of surface cracking or a large residual strain in the SLS’s also caused the modulation-doped SLS’s to have lower mobilities.     

Electrical properties of InAlAs/InAsxP1-x/InP composite-channel modulation-doped structures grown by solid source molecular beam epitaxy

We report on the electrical characteristics of the two-dimensional electron gas (2DEG) formed in an InAlAs/InAs_xP_1-x/InP pseudomorphic composite-channel modulation-doped (MD) structure grown by solid source (arsenic and phosphorus) molecular beam epitaxy (SSMBE). The As composition, x, of strained InAs_xP_1-x was determined by x-ray diffraction analysis of InP/InAs_xP_1-x/InP multi-quantum wells (MQWs) with compositions of x=0.14 to x=0.72. As the As composition increases, the room temperature sheet resistance of InAlAs/InAs_xP_1-x/InP composite-channel MD structures grown over a range of As compositions decreased from 510 to 250 Ω/cm², resulting from the greater 2DEG confinement and lower electron effective mass in the InAs_xP_1-x channel as x increases. The influence of growth conditions and epitaxial layer designs on the 2DEG mobility and concentration were investigated using 300 K and 77 K Hall measurements. As the exposure time of the As₄ flux on the growth front of InAs_xP_1-x increased during growth interruptions, the 2DEG mobility, in particular the 77K mobility, was considerably degraded due to increased roughness at the InAlAs/InAs_xP_1-x interface. For the InAlAs/InAs_0.6P_0.4/InP composite-channel MD structure with a spacer thickness of 8 nm, the room temperature 2DEG mobility and density were 7200 cm²/Vs and 2.5 × 10¹² cm⁻², respectively. These results show the great potential of the InAlAs/InAs_xP_1-x/InP pseudomorphic composite-channel MD heterostructure for high frequency, power device applications.     

Growth of GaAs1−xPx/GaAs and InAsxP1−x/InP strained quantum wells for optoelectronic devices by gas-source molecular beam epitaxy

In this paper we show that pseudomorphically strained heterostructures of InAs _x P_1−x /InP may be an alternative to lattice-matched heterostructures of In_1−x Ga _x As _y P_1−y /InP for optoelectronic applications. We first studied the group-V composition control in the gas-source molecular beam epitaxy (GSMBE) of the GaAs_1-x P _x /GaAs system. Then we studied GSMBE of strained InAs _x P_1−x /InP multiple quantum wells with the ternary well layer in the composition range 0.15 <x < 0.75. Structural and optical properties were characterized by high-resolution x-ray rocking curves, transmission electron microscopy, absorption and low-temperature photoluminescence measurements. High-quality multiple-quantum-well structures were obtained even for highly strained (up to 2.5%) samples. The achievement of sharp excitonic absorptions at 1.06, 1.3 and 1.55μm at room temperature from InAs _x P_1−x /InP quantum wells suggests the possibility of long-wavelength optoelectronic applications.     

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.     

Characterization of InP grown by OMVPE using trimethylindium and tertiarybutylphosphine (TBP) at low V/III ratios and reduced TBP partial pressures

We report an OMVPE growth process for InP using trimethylindium (TMI) and tertiarybutylphosphine (TBP), a V/III ratio of 15, and a TBP partial pressure of 0.5 Torr. Growth is initiated with a 0.1 μm buffer layer employing a ramped TBP flow. Results are presented for InP grown with two different samples of both TMI and TBP and compared to previous experimental results and theoretical predictions. Good surface morphology is obtained from 540 to 600° C. The net carrier concentrations, N_d-N_a, decrease with increasing growth temperature—but never fall below 1.3 × 10¹⁶ cm^-3. Mobilities of 3990 and 11200 cm²/V.sec are observed at 300 and 77 K, respectively. At 77 K, we infer a compensation ratio of ∼0.4, independent of N_d-N_a. Photoluminescence measurements at 6 K show intense near bandgap emission with a full width half maximum proportional to N_d-N_a. Weak emission is also observed from carbon acceptors, independent of growth temperature. Secondary ion mass spectroscopy measurements are performed on an InP wafer grown with four different temperatures. The observed sulfur concentration drops from 1 × 10¹⁸ to 6 × 10¹⁶ cm^-3 with increasing growth temperature. This confirms that sulfur is an important residual impurity in TBP. The observed carbon concentration is 4–6 × 10¹⁶ cm^-3, regardless of growth temperature.     

Metalorganic InP and Inx Ga1-x,Asy P1-y,on InP epitaxy at atmospheric pressure

We present a procedure for the MOVPE of InP as simple as the one currently used for GaAs. InP and InGaAsP alloys are grown on InP substrates using trimethy1indium (TMI), phosphine, trimethylgallium (TMG) and arsine. The choice of carrier gas is important ; a mixture of hydrogen and nitrogen allowed us to grow uniform layers over large areas at atmospheric pressure, without pyrolizing the phosphine or separating the input reactants. Preliminary characterization results are presented. Most information contained in this paper was presented at the 1983 Electron Materials Conference as paper Cl.     

Selective growth of InP on patterned,nonplanar InP substrates by low-pressure organometallic vapor phase epitaxy

The effects of indium sources, mask materials and etched mesa profiles on growth mor-phology of Fe-doped semi-insulating InP on patterned, nonplanar InP substrates were studied for low-pressure organometallic vapor phase epitaxy (OMVPE). The presence or absence of polycrystalline InP layers deposited on the mask was found to depend on the indium source but not on the mask material. Trimethylindium was found to be the preferable indium source for prevention of polycrystalline InP deposits on the mask. The etched mesa shape was found to dominate the final geometry of the OMVPE re-grown InP layer. Inclusion of an interfacial layer of 1.16 μm bandgap wavelength InGaAsP between the dielectric mask and InP substrate produces a favorable mesa shape by con-trolling the level of undercut during mesa etching, so as to form a smooth mesa profile. After selective regrowth of InP over the resulting mesa, a planar surface is typically achieved for mesa stripes with a mask overhang length as long as 2.6 μm and a mesa height as high as 4 μm.     

OMVPE growth of InP and Ga0.47ln0.53as using ethyldimethylindium

We report the organometallic vapor phase epitaxial (OMVPE) growth of InP and Ga_0.47In_0.53As using a new organometallic indium source, ethyldimethylindium (EDMIn), rather than the traditional sources triethylindium (TEIn) or trimethylindium (TMIn). EDMIn is a liquid at room temperature and its vapor pressure at 17° C was found to be 0.85 Torr using thermal decomposition experiments. The growth results using EDMIn were compared to those using TMIn in the same atmospheric pressure reactor. For InP, use of EDMIn resulted in a high growth efficiency of 1.3 × 10⁴ μm/ mole, which was independent of the growth temperature and comparable to the growth efficiency obtained with TMIn. The high growth efficiency is consistent with the observation of no visible parasitic gas phase reactions upstream of the substrate. The 4K photoluminescence (PL) spectra consist of a peak due to bound excitons and an impurity related peak 38 meV lower in energy. This impurity peak is ascribed to conduction band to acceptor transitions from carbon, due to the decreasing relative intensity of this peak with increasing V/III ratio. The relative intensity of the C impurity peak decreases by five times when the growth temperature is increased from 575 to 675° C, with a corresponding increase in the room temperature electron mobility from 725 to 3875 cm²/ Vs. For GalnAs lattice-matched to InP, use of EDMIn also resulted in a temperatureindependent high growth efficiency of 1.0 x 10⁴ μm/mole, indicating negligible parasitic reactions with AsH₃. The In distribution coefficient was nearly constant at a value of 0.9, however the run to run composition variation was slightly higher for EDMIn than for TMIn. The 4K PL showed donor-acceptor pair transitions due to C and Zn. The C impurity peak intensity decreased dramatically with increasing growth temperature, accompanied by an increase in the room temperature electron mobility to 5200 cm²/Vs. Overall, the growth of both InP and GalnAs using EDMIn was qualitatively similar to that using TMIn, although the room temperature electron mobilities were lower for the new source than for our highest purity bottle of TMIn.     

Use of tertiarybutylphosphine for OMVPE growth of (AlxGa1-x)o.51 In0.49P

This paper reports the results of atmospheric pressure organometallic vapor phase epitaxial growth of (Al _x Ga_1-x )_{0.51 0.49}P thin films using tertiarybutylphosphine (TBP) as the phosphorus source. The trimethylalkyls were used as group III sources. The growth temperature was 680° C. It was observed that V/III ratio dramatically affected the surface morphology and photoluminescence (PL). The epilayers grown at a V/III ratio lower than 60 had rough surfaces and weak PL emission. An input V/III ratio larger than 70 was required to obtain good surfaces and strong PL emission. Good quality (Al_xGa_1-x )_{0.51 0.49}P epilayers forx ≤ 0.62 were obtained at a V/III ratio of 85. The surface morphologies were smooth except for the occurrence of dense oval-shaped hillocks forx > 0.42. The Al distribution coefficient using TBP is the same as for phosphine (PH₃), which was used as the phosphorus source in previous AlGalnP growth. No parasitic reactions between TBP and trimethylalkyls were observed. 10 and 300 K PL emission was observed for all epilayers withx ≤ 0.62. However, the PL peak energy did not follow the band gap, as obtained for (Al_xGa_1-x )_{0.51 0.49}P epilayers grown using PH₃. The PL peak energy at both 10 and 300 K increased with increasingx forx ≤ 0.35, and then became nearly constant with further increases inx. In this region the PL is believed to be from a process involving a deep energy level, induced by an impurity from the TBP, bound to theX conduction band minimum. It was concluded that TBP has the potential to replace PH₃ for OMVPE growth of Al-containing compounds, although the purity needs to be improved.     

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.     

Properties of Ge-doped GaAs and Alx Ga1−xAs,Sn-doped Alx Ga1−xAs and Si-Te-doped GaAs

In order to better understand the electrical and optical properties of GaAs and Al_xGa_1-x As used in making double heterojunction lasers, we have studied the Hall coefficient, resistivity and photoluminescence behavior of doped epitaxial samples of these materials. In particular, we report results on Ge-doped GaAs and Al_x Ga_1-x As, Sn-doped Al_xGa_1-x As and Si-Te-doped GaAs single crystal layers which were grown on GaAs substrates by the liquid phase epitaxial method. The effects of impurities in the solution on the carrier concentration, mobility, photoluminescence spectra and possible recombination processes in these layers are discussed.     

Optimization studies of CVD growth of GaAs0.6P0.4

CVD growth conditions, particularly growth temperature and partial pressures of the reactant gases, strongly affect the growth characteristics and properties of GaAs_0.6P_0.4 epitaxial layers grown on GaAs substrates. For LED’s the most important properties of the material are B/J (brightness per unit current density) and surface morphology. This paper presents the results of a systematic study of the effect of temperature and reactant gas partial pressure (at a fixed III/V ratio) on B/J, surface morphology, growth rate, impurity doping and layer composition. Growth conditions which yield the optimum properties for LED’s are determined. The results are interpreted on the basis of kinetic and thermodynamic mechanisms controlling the growth process under various growth conditions. At constant temperature and constant III/V ratio, increasing the partial pressures causes the growth process to change from mass transport limited, where the growth rate increases with increasing partial pressures, to kinetically limited, where the growth rate is independent of partial pressures. Good morphology layers are obtained over a range of partial pressures around the transition from mass transport limited to kinetically limited growth. The B/J peaks at a value of partial pressure in the kinetically limited regime at which good morphology layers are obtained. Although B/J increases with increasing growth rate in the mass transport regime, the maximum B/J occurs in the region where growth rate is independent of partial pressures so that growth rate alone is not sufficient to determine B/J. In contrast to the “parabolic≓ dependence of growth rate on growth temperature, caused by the transition from the mass transport regime to the kinetic regime, the relative incorporation of As, P, and Te varies with temperature in the manner predicted from thermodynamics in both regimes. This behavior is consistent with the growth rate in the kinetic regime being limited by the desorption of chlorine atoms from the growth surface, with the reaction of As, P, and Te with the Ga proceeding thermodynamically at all temperatures.     

Liquid phase epitaxial growth of InAs1-xSbx on GaSb

Reported here, for the first time, is the lattice matched growth of InAs_1-xSb_x on GaSb. The thermodynamic incompatibility of the system, i.e., the strong tendency for the In-As-Sb liquid to dissolve the GaSb substrate, was solved via a novel liquid phase epitaxial growth technique. Liquid compositions for lattice matching conditions have been determined in the 400-600°C range. Epitaxial growth has been examined for (100), (111)B and (111)A orientations. Dislocation etch pit densities for lattice matched, and near lattice matched conditions are shown to be less than 10⁴-cm⁻² and 10⁵-cm⁻⁴, respectively. The composition of the epitaxial layers are determined by the Gandolfi X-ray diffraction technique and compositional homogeneity has been confirmed by SEM X-ray analysis. Some material related device properties which demonstrate the reproducibility of the growth technique are presented.     

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.     

Tertiarybutylarsine and tertiarybutylphosphine for the MOCVD growth of low threshold 1.55 μm InxGa1-xAs/InP quantum-well lasers

Tertiarybutylarsine (TBA) and teriarybutylphosphine (TBP) are liquid organometallic sources that are a safer alternative to arsine and phosphine. In this work, we have grown high-quality In_0.53Ga_0.47As/InP quantum wells at a temperature of 590° with TBA and TBP partial pressures of 0.4 and 2.5 Torr, respectively. A low-temperature photoluminescence study indicated optimized column V growth interruption times of 0.5 s for In_0.53Ga_0.47As wells with InP barriers. Using the optimized growth conditions, we have obtained lattice matched In_0.53Ga_0.47As/In_xGa_1-xAs_yP_1-x single quantum-well lasers emitting at 1.55 μm. Broad-area devices with a length of 3.5 mm exhibit a low threshold current density of 220A/cm². Broad-area lasers containing four quantum wells had a threshold current density of 300A/cm² for a 3.0 mm cavity length and CW powers of 40 mW per facet for an as-cleaved 4 × 750 μm device.     

Investigation of GaAs]-x_x P crystals using the pseudo-kossel X-ray and photoluminescence techniques

Two indirect methods of determining composition in GaAs_{1-x x}P films grown epitaxially on GaAs substrates are discussed in this paper. In the first method precision lattice parameters, obtained using the pseudo-Kossel technique in back reflection, are compared to compositions determined with the electron microprobe. A plot of corrected lattice parameter vs. %GaP (microprobe) over the range of composition investigated (0.10 < x < 0.55) shows that Vegard’s law holds very closely in this system. The slope of the line is -0.002042 Å/%GaP while the intercept is within 0.028% of the established lattice parameter for GaAs. No point lies farther than 0.003 Å from the line describing Vegard’s law.     

AFM observation of OMVPE grown ErP on InP (0 0 1), (1 1 1)A and (1 1 1)B substrates

ErP has been grown on InP (0 0 1), (1 1 1)A and (1 1 1)B substrates by low-pressure organometallic vapor-phase epitaxy. The morphological change with growth temperature has been explored by atomic force microscope. On all the substrates, ErP is grown in island structure. Height and area size of the ErP islands on (1 1 1)A substrate exhibit an obvious dependence on growth temperature. ErP islands grown at 540°C, that is the suitable temperature for ErP formation, gather to step edges to make wires.     

Horizontal unseeded vapor growth of Iv-Vi compounds and alloys

Large, high-quality crystals of various Pb-salt compounds and alloys have been grown from the vapor by a horizontal, unseeded, closed-tube method. The optimum growth conditions have been experimentally determined. The crystalline imperfections and electrical properties of the crystals were examined. In a series of growth experiments on PbTe, the source materials were prepared by adding small quantities of Pb to much larger quantities of zone-melted PbTe. This method makes it possible to control the source and as-grown crystal compositions for excess Pb or Te concentrations in the 10¹⁸/cm³ range. From the results of these experiments it was found that the composition of zone-melted PbTe (i. e., the maximum-melting point composition of PbTe) corresponds to a hole concentration of approximately 1 x l0¹⁹/cm³. This work was sponsored by the Department of the Air Force.     

基于InP衬底的晶格失配In0.68Ga0.32As的MOCVD生长及其特性研究

采用MOCVD生长技术在InP衬底上成功实现了晶格失配的3μm In0.68 Ga0.32As薄膜生长.通过As组分的改变,利用张应变和压应变交替补偿的InAsxP1-x应变缓冲层结构来释放由于晶格失配所产生的应力,在InP衬底上得到了与In0.68Ga0.32 As晶格匹配的InAsxP1-x“虚拟”衬底,通过对缓冲层厚度的优化,使应力能够在“虚拟”衬底上完全豫弛.通过原子力显微镜(AFM)、高分辨XRD、透射电镜(TEM)和光致发光(PL)等测试分析表明,这种释放应力的方法能够有效提高In0.68 Ga0.32 As外延层的晶体质量.     

Molecular beam epitaxy of CdTe and Hg1-xCdxTe ON GaAs (100)

Using the molecular beam epitaxial (MBE) technique, CdTe and Hg_1-xCd_xTe have been grown on Cr-doped GaAs (100) sub-strates. A single effusion cell charged with polycrystal-line CdTe is used for the growth of CdTe films. The CdTe films grown at 200 °C with a growth rate of ~ 2 μm/hr show both streaked and “Kikuchi” patterns, indicating single crystalline CdTe films are smoothly grown on the GaAs sub-strates. A sharp emission peak is observed at near band-edge (7865 Å, 1.577 eV) in the photoluminescence spectrum at 77 K. For the growth of Hg_1-xCd_xTe films, separate sources of HgTe, Cd and Te are used. Hg_0.6Cd_0.4Te films are grown at 50 °C with a growth rate of 1.7 μm/hr. The surfaces are mirror-smooth and the interfaces between the films and the substrates are very flat and smooth. As-grown Hg_0.6Cd_0.4Te films are p-type and converted into n-type by annealing in Hg pressure. Carrier concentration and Hall mobility of an annealed Hg_0.6Cd_0.4Te film are 1 × 10¹⁷ cm^?3 and 1000 cm²/V-sec at 77 K, respectively.