Structural and optical properties of GaxIn1−xP layers grown by chemical beam epitaxy

Chemical beam epitaxial (CBE) Ga_xIn_1?xP layers (x≈0.5) grown on (001) GaAs substrates at temperatures ranging from 490 to 580°C have been investigated using transmission electron diffraction (TED), transmission electron microscopy, and photoluminescence (PL). TED examination revealed the presence of diffuse scattering 1/2{111}_B positions, indicating the occurrence of typical CuPt-type ordering in the GaInP CBE layers. As the growth temperature decreased from 580 to 490°C, maxima in the intensity of the diffuse scattering moved from ½{111}_B to ½{?1+δ,1?δ,0} positions, where δ is a positive value. As the growth temperature increased from 490 to 550°C, the maxima in the diffuse scattering intensity progressively approached positions of $\frac{1}{2}\{\bar 110\} $ , i.e., the value of δ decreased from 0.25 to 0.17. Bandgap reduction (～45 meV) was observed in the CBE GaInP layers and was attributed to the presence of ordered structures.     

Growth of direct bandgap GalnP quantum dots on GaP substrates

GaInP has a direct bandgap for In concentrations higher than approximately 30%, and the band-lineup between GaInP and GaP is type-II for In concentrations less than 60%. Therefore, in order to use GaInP as the active light-emitting layer in an optoelectronic device grown on GaP, the strain induced by the lattice mismatch between GaInP and GaP has to be somehow managed such that formation of crystal defects is suppressed. One method is to grow the layer thinner than the critical thickness. Another method that recently received much attention is to grow strain-induced Stranski-Krastanov islands (sometimes referred to as self-assembled quantum dots). Small droplets of highly latticmismatched materials have been embedded into single crystals without generating defects such as threading dislocations and stacking faults using this method. We have grown a series of GaInP/GaP layers by metalorganic chemical vapor deposition and have studied the light emission from them. Ordered GaInP islands were found to be responsible for the light emission. We present the light emission characteristics of these ordered GaInP/GaP islands, and their dependence on various growth parameters.     

High quality GaAs/AlGaAs quantum wells grown on (111)A substrates by metalorganic vapor phase epitaxy

Growth of GaAs and AlGaAs epitaxial layers on both (111)A and (111)13 faces of GaAs substrates was studied by the atmospheric metalorganic vapor phase epitaxy (MOVPE) technique. We show that GaAs and AlGaAs layers with excellent surface quality can be grown at relatively low temperatures and V/III ratios (600°C, 15) on the (111)A face, whereas for layers on the (111)13 face a higher growth temperature (720°C) was required. GaAs/AlGaAs quantum well (QW) structures were successfully grown for the first time on the (111)A GaAs face by the MOVPE technique. The effects of various growth conditions on the surface morphology of the epilayers were studied. For the (111)A surface a wide growth window with temperatures in the range 600°-660°C and V/III ratios varying from 15 to 45 was established for obtaining excellent surface morphology. The properties of the QWs were investigated by high resolution X-ray diffractometry, photoluminenscence and photoreflectance measurements. These measurements indicate that the QWs are of very high structural and optical quality.     

Selective growth experiments on gallium arsenide (1 0 0) surfaces patterned using UV-nanoimprint lithography

We describe a nanoimprint lithography (NIL) process and subsequent solid-source molecular beam epitaxy (SSMBE) growth of III–V semiconductors on patterned substrates. In particular, growth of GaAs, GaInAs, and GaInP, and effects of growth temperature were studied using AFM, SEM, and XRD. It turns out that selective growth of GaAs on patterned substrates is relatively straightforward, but GaInAs and GaInP are more challenging. For the first time, GaInP has been selectively grown on UV-NIL-patterned substrates using SSMBE.     

Effects of group V precursor and step structure on ordering in GaInP

The effects of the P precursor have been studied for GaInP layers grown at 670°C on singular (001) GaAs substrates. Use of either of the two precursors, tertiarybutylphosphine (TBP) and phosphine (PH₃), for the organometallic vapor phase epitaxial growth, has been shown to result in the same degree of CuPt order in the epitaxial layers. However, the steps on the surface are mainly bilayers, approximately 5.8Å in height, for growth using TBP and mainly monolayers for growth using PH₃. This indicates that the step structure plays no role in the ordering process occurring on the surface during growth. Examination of the spacing between these surface steps vs the input partial pressure of the P precursor indicates that neither the surface diffusion coefficient nor the sticking coefficients of group III adatoms at the step edge is dependent on the P precursor. This suggests that the step structure also has no effect on the sticking coefficient.     

Localized deposition of GaAs/GaInP heterostructures using LP-MOVPE

GaInP layers were grown selectively by low pressure MOVPE in patterned SiO₂ masks on GaAs (100) substrates. The variation of the composition and spontaneous ordering phenomena were analysed by Raman spectroscopy and photoluminescence. In contrast to GaInAs, the composition of GalnP shows only a very weak dependence on the size of the structures. On the other hand, there is a shift of the bandgap energy up to 40 meV with decreasing size of the stripes caused by ordering of the Ga and In atoms. Based on these findings lattice matched GaAs/GalnP multilayers were grown to delineate the growth history of the structures. It was demonstrated that the growth habit of deposition in narrow slits (>1μm) can be used to produce mesa-like stripes with dimensions below 100 nm on top of the mesa. Results of GaAs/GaInP quantum wells selectively grown on top of a mesa are presented.     

A comparative study of GaInP/GaAs heterojunction bipolartransistors grown by CBE using TBA/TBP andAsH3/PH3 sources

GaInP/GaAs heterojunction bipolar transistors (HBT's) have been fabricated on epitaxial layers grown by chemical beam epitaxy (CBE) using an all metalorganic approach. Reduced toxicity tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) were used for group V sources. DC results showed good base and collector current ideality factors of 1.23 and 1.05 respectively. The maximum DC current of 50 was obtained. A comparison of these results with HBT characteristics obtained using AsH ₃/PH₃ or TBA/PH₃ demonstrates the feasibility of replacing the toxic AsH₃ and PH₃ by less toxic TBA and TBP sources in the growth of GaInP/GaAs HBT's     

Incorporation behaviour of carbon and silicon on (100) and (111) surfaces during growth of GaAs/GaAs and Ga0.47In0.53As/InP by molecular beam epitaxy

Silicon and carbontetrabromide were used as dopant sources in the growth of GaAs/GaAs and Ga_0.47In_0.53As/InP structures. We studied the incorporation behaviour of these group IV atoms on (100) and {111} surfaces as a function of growth temperature. The free carver concentrations determined by Hall measurements for Si-doped GaAs and Ga_0.47In_0.53As layers are independent of growth temperature on all surface orientations studied. Silicon acts fundamentally as a donor except, as expected, for doped layers on (111)A GaAs substrates, where it acts as an acceptor. Carbon incorporation in GaAs and Ga_0.47In_0.53As always results in a p-type conduction independent of the surface orientations (100)/{111} or the growth temperatures we used. In contrast to the results on GaAs, carbon shows a strong temperature-dependent activation in Ga_0.47In_0.53As grown on (100) and (111)B surfaces. Carbon-doped Ga_0.47In_0.53As on (111)A and carbon-doped GaAs layers on (100)/{111} GaAs surfaces exhibit only a very weak dependence of the carrier concentration on the growth temperature. A significant amphoteric behaviour of carbon was not observed in any of the materials investigated.     

GaInAsP过渡层在808 nm GaAsP/(Al)GaInP半导体激光器中降电压的应用

利用金属有机化学气相沉积的方法在GaAs衬底上生长了GaInAsP外延层及GaAsP/(Al)GaInP激光器外延层。生长的GaInAsP外延层与GaAs晶格匹配,并且带隙处于Ga_0.5In_0.5P与GaAs中间。在GaInP/GaAs异质结界面插入此结构的GaInAsP过渡层,可以有效的降低异质结的带阶,尤其是价带带阶。相比于突变GaInP/GaAs异质结的808 nm GaAsP/(Al)GaInP半导体激光器,含有GaInAsP过渡层的半导体激光器具有更低的工作电压。因此,在350 mW输出功率下,半导体激光器的功率转换效率由52%提高至60%。并且在大电流注入下,含有GaInAsP过渡层的半导体激光器由于产生的焦耳热减少,具有更高的输出功率。     

Influence of GaInP ordering on the performance of GaInP solar cells

CuPt-type ordering with undesirable properties always occurs in GaInP at growth conditions that are very close to those leading to the highest quality material in metal organic chemical vapor deposition. In this work, highly disordered GaInP with high crystalline quality was obtained by optimizing growth conditions. Room-temperature and low-temperature photoluminescence (PL) spectra of AlGaInP/GaInP/AlGaInP double heterostructures (DHs) reveal that the band edge emission intensity is enhanced by optimizing growth temperature, V/III ratio, and reactor pressure at the expense of low energy peak originating from spatially indirect recombination due to the ordering-related defects. The DH sample with less ordering-related defects demonstrates a longer effective minority carrier lifetime, consequently, the GaInP solar cell shows a significant improvement in the performance.     

Si衬底上无坑洞3C-SiC的外延生长研究

在冷壁式不锈钢超高真空系统上 ,利用低压化学气相淀积 (LPCVD)方法在直径为 5 0 mm的单晶 Si(1 0 0 )和 Si(1 1 1 )晶向衬底上生长出了高取向无坑洞的晶态立方相碳化硅 (3 C-Si C)外延材料 ,利用反射高能电子衍射 (RHEED)和扫描电镜 (SEM)技术详细研究了 Si衬底的碳化过程、碳化层的表面形貌及缺陷结构 ,获得了界面平整光滑、没有空洞形成的 3 C-Si C外延材料 ,并采用 X-射线衍射 (XRD)、双晶 X-射线衍射 (DXRD)和霍尔(Hall)测试等技术研究了外延材料的结构和电学特性     

Spatially resolved Raman investigation of Si-doped GaAs layers on patterned GaAs(100) substrates grown by molecular beam epitaxy

Local carrier transport properties of Si-doped GaAs layers on ridge structures exhibiting (111)A and (111)B sidewalls are investigated. The layers were grown by molecular beam epitaxy at different substrate temperatures and As/Ga flux ratios. Using spatially resolved Raman spectroscopy we determine the type and density of free charge carriers (≥ 5 × 10¹⁷ cm⁻³) in the grown layers on the different index facets from an analysis of the coupled plasmon-longitudinal optical-phonon mode which was calibrated against Hall standards. We demonstrate that on the (100) and (111)B facets the regrown layers are n-type and on the (111)A facets p- or n-type depending on the growth conditions. Line scans of the carrier density show that the (100)/(111)A/(100) facet transition forms a graded lateral n-p-n junction. Spatially resolved photoluminescence measurements confirm our findings.     

CdZnTe衬底对碲镉汞气相外延表面形貌的影响

利用气相外延技术在CdZnTe衬底上生长Hg1-xCdxTe薄膜材料,通过在不同晶向、不同极性、不同晶向偏离角度CdZnTe衬底上的外延结果发现,CdZnTe衬底对外延形貌的影响非常大。(111)面衬底上外延形貌明显优于(211)面衬底的外延形貌。对于同是<111>CdZnTe晶向的衬底,(111)Cd面CdZnTe衬底上的外延形貌明显优于(111)Te面。对于(111)Cd面CdZnTe衬底,当晶向偏离角度不同时,其外延形貌也有差异,晶向偏离角越小表面形貌越好。     

Determining the [001] crystal orientation of CdTe layers grown on (001) GaAs

We discuss various possibilities for determining the orientation of CdTe layers grown on (001) GaAs and in particular, determining the (001) orientation. This growth orientation is characterized by a three dimensional growth mechanism which controls the growth in the (111) orientation. We show that a thin layer of ZnTe deposited directly on the oxide free GaAs surface can be used to determine the (001) orientation, eliminate (111) phases and enhance a two dimensional growth of the CdTe layer, resulting in an improved crystalline quality and a smooth surface morphology. CdTe layers grown in the (111) direction on oxide free (001) GaAs substrates contain (111) microtwins and an intermixed (001) phase. This work is a part of a Ph.D. thesis to be submitted to the Weizmann Institute of Science.     

Effects of growth rate and mercury partial pressure on twin formation in HgCdTe (111) layers grown by metalorganic chemical vapor deposition

The relationship between twin formation and the growth conditions for (111) HgCdTe epitaxial layers grown by metalorganic chemical vapor deposition was investigated. The existence of twins was confirmed by x-ray diffraction and cross-sectional transmission electron microscopy. The x-ray diffraction intensity of the 180°ø rotated 422 asymmetric reflection with that of the 422 asymmetric reflection was compared to detect the presence of twins. The layer obtained using a low growth rate and a low Hg partial pressure showed double-positioning (DP) twins. The twins became lamellar as the growth rate increased. Twin-free HgCdTe epitaxial layers were obtained under a high growth rate and a high Hg partial pressure. These results suggest a model for twin formation based on the difference in the growth mechanism of HgTe and CdTe. Twin-free (111) HgCdTe epitaxial layers were reproducibly obtained without using inclined substrates by optimizing the growth conditions by using this model.     

Flat GaN epitaxial layers grown on Si(111) by metalorganic vapor phase epitaxy using step-graded AlGaN intermediate layers

In this work, we report on the growth by metalorganic vapor phase epitaxy (MOVPE) of GaN layers on AlN/Si(111) templates with step-graded AlGaN intermediate layers. First, we will discuss the optimization of the AlN/Si(111) templates and then we will discuss the incorporation of step-graded AlGaN intermediate layers. It is found that the growth stress in GaN on high-temperature (HT) AlN/Si(111) templates is compressive, although, due to relaxation, the stress we have measured is much lower than the theoretical value. In order to prevent the stress relaxation, step-graded AlGaN layers are introduced and a crack-free GaN epitaxial layer of thickness >1 μm is demonstrated. Under optimized growth conditions, the total layer stack, exceeding 2 μm in total, is kept under compressive stress, and the radius of the convex wafer bowing is as large as 119 m. The crystalline quality of the GaN layers is examined by high-resolution x-ray diffraction (HR-XRD), and the full-width-at-half maximums (FWHMs) of the x-ray rocking curve (0002) ω-scan and (−1015) ω-scan are 790 arc sec and 730 arc sec, respectively. It is found by cross-sectional transmission electron microscopy (TEM) that the step-graded AlGaN layers terminate or bend the dislocations at the interfaces.     

The effect of substrate tilt on MOCVD growth of {100}CdTe on {100}GaAs

Epitaxial layers of CdTe were grown by metalorganic chemical vapor deposition on surfaces of single crystal, {100} GaAs which had been ground, polished, and etched to a spherically shaped done. This dome-shaped surface allowed the morphological and structural properties of the epitaxial CdTe layers to be determined for all 360° of azimuth and up to 15° of polar angle from the [100] axis within a single growth experiment. At two growth temperatures, approximately 275 and 375°C, the results show distinct twofold rotational symmetry in both morphology and crystal perfection as determined by x-ray rocking curve measurement. Surface morphology is superior at azimuths near tilts toward the <111>A pole. Four-sided pyramidal hillocks appear at other azimuths and at 0° tilt; the symmetry of the hillocks diminishes as the tilt increases. The orientations for growth which simultaneously minimize the surface defects and rocking curve full-width half-maximum appear to be at locations on the surface where the surface normal is tilted 3–4° toward the <111>A or <111>B, depending on the temperature regime chosen. Epitaxial layers grown on planar wafers of {100}GaAs tilted toward <111>Ga and <111>As show surface morphology essentially identical to the dome at these orientations. The surface morphology of CdTe growth on GaAs/Si wafers suggests that these layers are tilted toward the <111>B.     

The Growth of Transition Metals on H‐Passivated Si(111) Substrates

The growth of Co and Ag layers on wet‐processed H‐passivated Si(111) substrates by molecular beam epitaxy (MBE) has been studied using high resolution scanning tunneling microscopy (STM) with regard to possible applications of the layers in magnetoelectronic devices. Roughness and intermixing at interfaces as functions of deposition temperature and layer thickness are key parameters for the performance of such devices. The initial growth of Co and Ag and the influence of Ag atoms on the Si(111) surface reconstructions provide insight into adatom–substrate interactions.     

Study of minority carrier diffusion lengths in photoactive layers of multijunction solar cells

A technique for determining a minority carrier’s diffusion length in photoactive III–V layers of solar cells by approximating their spectral characteristics is presented. Single-junction GaAs, Ge and multi-junction GaAs/Ge, GaInP/GaAs, and GaInP/GaInAs/Ge solar cells fabricated by hydride metal-organic vapor-phase epitaxy (H-MOVPE) have been studied. The dependences of the minority carrier diffusion length on the doping level of p-Ge and n-GaAs are determined. It is shown that the parameters of solid-state diffusion of phosphorus atoms to the p-Ge substrate from the n-GaInP nucleation layer are independent of the thickness of the latter within 35–300 nm. It is found that the diffusion length of subcells of multijunction structures in Ga(In)As layers is smaller in comparison with that of single-junction structures.