OMVPE growth of the metastable III/V alloy GaAs0.5Sb0.5

The two crystal growth parameters most likely to affect the occurrence of GaAs_0.5Sb_0.5 spinodal decomposition during organometallic vapor phase epitaxial (OMVPE) growth, substrate temperature and substrate orientation, were investigated in detail. The temperature range studied was the widest over which good morphology layers could be grown, from 550 to 680° C. The InP substrate orientations used were (100), (221) and (311). The growth process was found to be diffusion controlled at high temperatures, but to be controlled by surface kinetics at temperatures below approximately 620° C, depending on substrate orientation. Growth of high quality layers was found to be much easier between 570 and 640° C. In addition, the 77 K PL intensity is much stronger for layers grown in this temperature range. The minimum PL halfwidth at 77 K is 20 meV and at 8 K is 16 meV. The typical room temperature hole mobilities are 100 cm²/Vs with hole concentrations of 2 x 10¹⁷ cm^-3 in undoped material. The temperature dependence of mobility is consistent with enhanced alloy scattering. Surprisingly, the growth temperature has no significant effect on either PL halfwidth or hole mobility between 560 and 660° C. The single Raman line observed for the unannealed alloy is split after annealing into two lines corresponding to the GaAs-rich and GaSb-rich alloys on either side of the range of solid immiscibility. The spinodal decomposition apparently starts at the surface where the coherency strain, which stabilizes the single phase alloy, is smallest.     

Some characteristics of highly N-doped VPE grown GaAs epilayers

The doping behaviour of S and Se in the VPE growth of GaAs at 760 and 660°C is studied by carrier concentra-tion, mobility, photo and cathodoluminescence measure-ments. The carrier concentration increases linearly with the partial pressure of S or H₂Se up to a solubi-lity limit, the highest value of which is obtained with Se at about 10¹⁹cm^-3. The mobility for Se-doped layers is higher than for S-doped ones when n > 4.10¹⁷cm^-3, and a mobility decrease is observed for both at dopings exceeding the solubility limit. Postgrowth annealing at the growth temperature of highly doped samples decreases their carrier concentration to values corresponding to the bulk solubility limit. The decrease of the room temperature luminescence intensity at high doping levels in tentatively interpreted as due to precipitate for-mation. Finally, the linear dependence on the dopant partial pressure of the impurity incorporation as well as the observed annealing behaviour are interpreted by an incorporation mechanism controlled by the surface states.     

The growth and characterization of uniform Ga1-xInxAs (X ≤.25) by Organometallic VPE

Compositionally uniform Ga_1-xIn_xAs epitaxial layers with 0 ≤ x ≤ 0.2 5 have been grown by organometallic VPE on ◃100▹ GaAs substrates. Compositional uniformities of ±0.25 InAs percentage and ±5% thickness over a 3-cm long wafer have been achieved and are essentially independent of small changes in reactor geometry such as the angle of the susceptor tilt or wafer position on the susceptor. Growth has also been demonstrated at x = 0.52. The Ga_1-xIn_xAs is grown using trimethylgallium (TMGa), triethylindium (TEIn) or trimethylindium (TMIn), and trimethylarsenic (TMAs). The use of TMAs eliminates the roomtemperature gas-phase reaction between AsH₃ and either TEIn or TMIn, and allows one atmospnere pressure growth conditions to be used without any special mixing arrangements in the reactor. The comparative effects of using TEIn or TMIn as the In source are discussed in terms of crystal quality. Data on crystal composition as a function of gas phase composition and growth rate as a function of composition are presented, and n doping and carrier mobilities and p doping of Ga_.80In_.20As ars characterized. The vapor pressure of TMIn at 0°C is determined to be 0.21 mmHg.     

用回熔再生长LPE工艺制备高效AlGaAs／GaAs太阳电池

报道了采用欠饱和溶液的回熔—再生长液相外延（ＬＰＥ）方法制备高效ＡＩｘＧａ１－ｘＡｓ／ＧａＡｓ异质结构太阳电池的工艺。研究表明，与传统的过冷生长技术相比，回熔工艺对衬底质量的要求不严格，且能形成有利于光生少子被收集的带隙结构。在工艺优化的情况下，获得大阳电池的全面积转换效率在ＡＭ０，１ｓｕｎ的测试条件下为１８．７８％（０．７２ｃｍ２），在ＡＭ１．５，１ｓｕｎ下为２３．１７％。     

A high‐efficiency LPE GaAs solar cell at concentrations ranging from 2000 to 4000 suns

III–V solar cells for terrestrial concentration applications are currently becoming of greater and greater interest. From our experience, concentrations higher than 1000 suns are required with these cells to reduce PV electricity cost to such an extent that this alternative could become cost competitive. In this paper, a single‐junction p/n GaAs solar cell, with efficiencies of 23ċ8 and 22ċ5% at concentration ratios of 2700 and 3600 suns respectively, is presented. This GaAs solar cell is well suited for use with non‐imaging optical concentrators, which possess a large aperture angle. Low‐temperature liquid phase epitaxy (LTLPE) has been the growing technique for the semiconductor structure as an attempt to use a simplified, cheap and clean technique, within a renewable energy perspective. The GaAs solar cell presented is compared with the highest efficiency tandem solar cells at concentration levels exceeding 1000 suns. The GaAs solar cell performance maintains high efficiencies up to 4000 suns, while tandem cells seem to drop very quickly after reaching their maximum. Therefore, single‐junction GaAs solar cells are a good candidate for operating at very high concentrations, and LPE is able to supply these high‐quality solar cells to work within terrestrial concentration systems, the main objective of which is the reduction of PV electricity costs. Copyright © 2003 John Wiley & Sons, Ltd.     

MOCVD growth of AlGaAs/GaAs structures on nonplanar {111} substrates: Evidence for lateral gas phase diffusion

We investigate the MOCVD growth characteristics of AlGaAs on nonplanar {111}A and {111}B substrates. Growth over features etched into the {111} substrates is found to be highly anisotropic and asymmetric. The ratio of growth rates on adjacent facets is strongly dependent on the depth of the etched feature during growth, and is strikingly different between AlGaAs and GaAs layers. These observations suggest a large difference in the surface chemistry of Al and Ga species under these growth conditions and indicate that the column III element determines the relative growth rates of different facets during nonplanar growth. The results also provide strong evidence that lateral gas phase diffusion of reactants can be perhaps more significant than surface migration as a mechanism determining the incorporation sites of column III elements. Growth characteristics on nonplanar {111} substrates are markedly different than those observed for nonplanar growth on {100} substrates, creating a new set of design tools for the single step growth of guided wave devices such as lasers, modulators and waveguides.     

Surface photoabsorption monitoring of the growth of GaAs and InGaAs at 650°C by MOCVD

By monitoring the cyclic behavior of surface photoabsorption (SPA) reflectance changes during the growth of GaAs at 650°C and with sufficient H₂ purging time between the supply of trimethylgallium and AsH₃, we have been able to achieve controlled growth of GaAs down to a monolayer. Our results show, as confirmed by photoluminescence (PL) measurements, the possibility of growing highly accurate quantum well heterostructures by metalorganic chemical vapor deposition at conventional growth temperatures. We also present our PL measurements on the InGaAs single quantum wells grown at this temperature by monitoring the SPA signal.     

重掺碳GaAs层的MOCVD生长及特性研究

采用 CCl4 作为碳掺杂源 ,进行了重掺碳 Ga As层的 L P- MOCVD生长 ,并且对掺杂特性进行了研究 ,研究了各生长参数对掺杂的影响。CCl4 流量是决定掺杂浓度的主要因素。减小生长温度、减小 / 比、降低生长压力 ,都能较大的提高掺杂浓度。通过改变 CCl4 流量 ,在生长温度为5 5 0～ 6 5 0℃、 / 比为 15～ 4 0 ,生长压力在 1× 10 4 ～ 4× 10 4 Pa的范围内 ,均能得到高于 2× 10 19/cm3 的掺碳 Ga As外延层 ,最高掺杂浓度为 8× 10 19/ cm3     

GaAs光电阴极的MOCVD法生长及其激活工艺研究

本文报道了用ＭＯＣＶＤ法生长出了有效的ＧａＡｓ光电阴极材料，并且在国产的ＧａＡｓ光电阴极激活系统上进行激活实验，其反射式积分灵敏度高于１０００μＡ／ｌｍ。     

Effect of oxygen injection during vpe growth of GaAs Films

The effect of oxygen injection during VPE growth of silicon doped and unintentionally doped GaAs has been investigated for the Ga-AsCl₃-H₂ process. Depending on the oxygen concentration a reduction in the carrier concentration of up to four orders of magnitude is found for the case of Si doping. Without purposely adding Si, oxygen injection yields high resistivity layers. Hall mobility data suggest that the simultaneous injection of both silicon and oxygen is also responsible for the introduction of a deep center which is probably associated with a Si-0 complex. We compared our results on carrier concentration with values calculated from a thermody-namic model in which both the injected SiH₄ and oxygen are taken into account. The computed behavior shows the same trend as our experimental data. This finding also provides further support for the validity of the silicon contamination model as an explanation of the background doping of VPE GaAs.     

快速率生长MBE InAs/GaAs(001)量子点

用快速率(1.0ML/s)生长MBE InAs/GaAs(001)量子点。原子力显微镜观察结果表明,在量子点体系形成的较早阶段,量子点密度N(θ)随InAs沉积量θ的变化符合自然指数形式N(θ)∝ek(θ-θc),这与以前在慢速生长(≤0.1ML/s)条件下出现的标度规律N(θ)∝(θ-θc)α明显不同。另外,在N(θ)随θ增加的过程中,快速率生长量子点的高度分布没有经历量子点平均高度随沉积量θ逐渐增加的过程。这些实验观察说明,以原子在生长表面作扩散运动为基础的生长动力学理论至少是不全面的,不适用于解释InAs量子点的形成。这些观察和讨论说明,即使在1.0ML/s的快速率生长条件下,量子点密度也可以通过InAs沉积量有效地控制在1.0×108cm-2以下,实现低密度InAs量子点体系的制备。     

A GeSi-buffer structure for growth of high-quality GaAs epitaxial layers on a Si substrate

A SiGe-buffer structure for growth of high-quality GaAs layers on a Si (100) substrate is proposed. For the growth of this SiGe-buffer structure, a 0.8-μm Si_0.1 Ge_0.9 layer was first grown. Because of the large mismatch between this layer and the Si substrate, many dislocations formed near the interface and in the low part of the Si_0.1Ge_0.9 layer. A 0.8-μm Si_0.05Ge_0.95 layer and a 1-μm top Ge layer were subsequently grown. The strained Si_0.05Ge_0.95/Si_0.1Ge_0.9 and Ge/Si_0.05Ge_0.95 interfaces formed can bend and terminate the upward-propagated dislocations very effectively. An in-situ annealing process is also performed for each individual layer. Finally, a 1–3-μm GaAs film was grown by metal-organic chemical vapor deposition (MOCVD) at 600°C. The experimental results show that the dislocation density in the top Ge and GaAs layers can be greatly reduced, and the surface was kept very smooth after growth, while the total thickness of the structure was only 5.1 μm (2.6-μm SiGe-buffer structure +2.5-μm GaAs layer).     

Selective area growth of GaAs with semiconductor-metal-semiconductor structures using pulsed-mode operation of MOCVD

Selective area growth of GaAs with semiconductor-metal-semiconductor structures using pulsed-mode operation of MOCVD, which controls the flow of trymethylgallium (TMG) at regular intervals, is reported. GaAs is selectively grown over tungsten gratings on (100) GaAs substrates. Tungsten gratings are masked with SiO₂ for the selective growth and it is possible to have good GaAs growth over W gratings without keeping the substrate temperature high and the growth rate low. The ideality factor and the barrier height of the W-GaAs Schottky diode in-situ annealed under the growth conditions show slight degradation with increased growth time. Using double crystal x-ray diffractometer and Auger electron spectroscopy analysis, it is shown that the interdiffusion of W and GaAs takes place. A vertical FET is fabricated to show the device application of this selective growth method.     

Group III alkyl source purity effect on the quality of GaAs grown with tertiarybutylarsine

We have grown unintentionally doped GaAs films using tertiarybutylarsine (tBAs) or arsine reacted with clean or silicon contaminated triethylgallium. Hall and SIMS data along with photoluminescence spectra show that the silicon contaminant level in GaAs MOCVD layers grown with tBAs is higher than for layers grown using arsine. Thus, high purity in the triethylgallium source is more critical for high purity GaAs films when using tBAs than when using arsine.     

Electron microscope studies of InxGav1−xAs/GaAs/Si grown by metalorganic chemical vapor deposition

The microstructure of In_xGa_1−xAs/GaAs (5 nm/5 nm, x < 0 to 1.0), as grown by a metalorganic chemical vapor deposition two-step growth technique on Si(100) at 450‡C, and subsequently annealed at 750‡C, is investigated using plan-view and cross-sectional transmission electron microscopy. The variations in resultant island morphology and strain as a function of the In content were examined through the comparison of the misfit dislocation arrays and moirés observed. The results are discussed in relation to the ways in which the island relaxation process changes for high In content.     

Metalorganic chemical vapor deposition growth and characterization of InGaP/GaAs superlattices

Lattice-matched In_0.49Ga_0.51P/GaAs superlattices were grown on (001) GaAs substrates using metalorganic chemical vapor deposition. The interface properties were characterized by photoluminescence, transmission electron microscopy, and x-ray diffraction. By varying the growth temperature, the precursor flow rates, and the growth interruption at the interfaces, we found that, while arsenic and phosphorus carry over have some effect on the formation of a low-bandgap InGaAsP quaternary layer at the interfaces, the In surface segregation seems to play an important role in the formation of the interface quaternary layer. Evidence of this indium segregation comes from x-ray and photoluminescence studies of samples grown at different temperatures. These studies show that the formation of an interfacial layer is more prominent when the growth temperature is higher. Growing a thin (∼1 monolayer thick) GaP intentional interfacial layer on top of the InGaP before the growth of the GaAs layer at the P→As transition effectively suppresses the formation of the low-bandgap unintentional interface layer. On the other hand, the growth of a thin GaAsP (or GaP) layer before the growth of the InGaP layer, at the As→P transition increases the formation of a low-bandgap interfacial layer. This nonequivalent effect of a GaP layer at the two interfaces on the PL properties is discussed.     

Atmospheric and low pressure shadow masked MOVPE growth of InGaAs(P)/InP and (In)GaAs/(Al)GaAs heterostructures and quantum wells

The shadow masked growth technique is presented as a tool to achieve thickness and bandgap variations laterally over the substrate during metalorganic vapor phase epitaxy. Lateral thickness and bandgap variations are very important for the fabrication of photonic integrated circuits, where several passive and active optical components need to be integrated on the same substrate. Several aspects of the shadow masked growth are characterized for InP based materials as well as for GaAs based materials. Thickness reductions are studied as a function of the mask dimensions, the reactor pressure, the orientation of the masked channels and the undercutting of the mask. The thickness reduction is strongly influenced by the mask dimensions and the reactor pressure, while the influence of the orientation of the channels and the amount of undercutting is only significant for narrow mask windows. During shadow masked growth, there are not only thickness variations but also compositional variations. Therefore, we studied the changes in In/Ga and As/P ratios for InGaAs and InGaAsP layers. It appears that mainly the In/Ga-ratio is responsible for compositional changes and that the As/P-ratio remains unchanged during shadow masked growth.     

基于低温In_xGa_(1-x)P组分渐变缓冲层的InP/GaAs异质外延

采用低温GaAs与低温组分渐变InxGa1-xP作为缓冲层,利用低压金属有机化学气相外延(LP-MOCVD)技术,在GaAs(001)衬底上进行了InP/GaAs异质外延实验。实验中,InxGa1-xP缓冲层选用组分线性渐变生长模式(xIn0.49→1)。通过对InP/GaAs异质外延样品进行双晶X射线衍射(DCXRD)测试,并比较1.2μm厚InP外延层(004)晶面ω扫描及ω-2θ扫描的半高全宽(FWHM),确定了InxGa1-xP组分渐变缓冲层的最佳生长温度为450℃、渐变时间为500s。由透射电子显微镜(TEM)测试可知,InxGa1-xP组分渐变缓冲层的生长厚度约为250nm。在最佳生长条件下的InP/GaAs外延层中插入生长厚度为48nm的In0.53Ga0.47As,并对所得样品进行了室温光致发光(PL)谱测试,测试结果表明,中心波长为1643nm,FWHM为60meV。     

The growth of buffered GaAs mesfet structures by LPE

Layers of LPE GaAs have been grown with background carrier levels in the low 10¹⁴ cm⁻³ range by systematic bakeouts of the Ga melts together with between-run loading in a dry N₂ environment. High resistivity layers in the range 10₃-10⁴Ω cm have been grown by making use of the compensation of free carriers by the out diffusion of Cr from the substrate. Intentional Cr-doping from the melt resulted in layers with poor surface morphologies. Buffered MESFET structures have been grown which show near ideal carrier concentration profiles and which do not exhibit interfacial space charge effects.     

The use of a metalorganic compound for the growth of InP-epitaxial layers

InP epitaxial layers have been grown by the pyro-lysis of a new metalorganic compound, a trimethyl-indium trimethyl-phosphene adduct. The formation of unwanted polymer products during epitaxial growth could be avoided in this way. The layers were grown at 500°C with a growth rate of about 1 μmh_-1. Net carrier concentrations of n≏5-10^l5cm^-3 could be achieved.