Adjusting trimethylgallium injection time to explore atomic layer epitaxy of GaAs between 425 and 500°C by organometallic vapor phase epitaxy

In experiments employing a conventional low-pressure, rotating-disk organome-tallic vapor phase epitaxy reactor, GaAs epilayers have been grown at substrate temperatures ranging from 425 to 500°C by exposing the substrate alternately to trimethylgallium (TMG) and AsH₃.The GaAs growth rateR was approximately constant with TMG flow rate, but with increasing TMG injection timet, it increased to more than one monolayer per TMG/AsH₃ cycle without saturating. Although growth was not self-limiting, for one specific combination of temperature andt, a value of R = 1 monolayer/cycle could be achieved by usingt values decreasing from 10.8 s at 425°C to 0.9 s at 500°C in accordance with an Arrhenius relationship between 1/t and absolute temperature.     

Selenium doping of GalnP by atomic layer epitaxy

Selenium doping of GalnP was performed using atomic layer epitaxy. The dependence of the n-type carrier concentration of Se-doped GalnP on growth temperature was quite different from that of Se-doped GaAs. Reducing growth temperature was found to be a crucial factor in achieving high n-type doping levels in as-grown Se-doped GalnP.     

Atomic layer epitaxy of InAs using tertiarybutylarsine

Tertiarybutylarsine and trimethylindium were used as precursors for atomic layer epitaxy of InAs. Self-limiting growth has been observed for a large temperature range between 350–410°C. In-situ reflectance difference spectroscopy was used to study the difference between the As and In self-limiting mechanisms on the InAs surface and also to optimize the growth parameters. Optical and transport properties of InAs grown epilayers show that high purity material can be achieved by atomic layer epitaxy.     

Growth of GaAs by vacuum atomic layer epitaxy using tertiarybutylarsine

We report the results of GaAs grown by vacuum atomic layer epitaxy using trimethylgallium (TMGa) and tertiarybutylarsine (TBAs) as the group III and V sources. The growth rate saturates at one monolayer per cycle for a wide range of growth parameters. The temperature window for monolayer growth is as wide as 70°C. All the films are p-type with the carrier concentration depending on the exposure conditions of TMGa and TBAs.     

Monitoring of CdTe atomic layer epitaxy using in-situ spectroscopic ellipsometry

Atomic layer epitaxy or ALE has proven to be useful for the growth of epitaxial layers of high uniformity, good quality, and well-controlled thickness. In this study, we have carried out in-situ monitoring during the atmospheric pressure ALE of CdTe on GaAs (100) substrates using spectroscopic ellipsometry (SE). The susceptor temperature, reactant partial pressures, as well as the flow and flush duration for each precursor are crucial process variables for ALE growth. Growth was carried out for 20–25 cycles under different sets of these process conditions during the experiment and in-situ SE was used to verify the presence of layer-by-layer growth, which enabled the quick determination of the process window. We observed ALE growth of CdTe at 300°C, supporting the explanation that the growth of CdTe occurs via a surface catalyzed decomposition of the Te precursor di-isopropyltelluride (DIPTe). Investigation of ALE mode growth behavior for different susceptor temperatures and DIPTe flush times indicated that the growth was limited by competition between desorption and reaction of the adsorbed DIPTe species on the Cd terminated surface.     

Improved CdTe layers on GaAs and Si using atomic layer epitaxy

In this paper, we report on the atomic layer epitaxy (ALE) of CdTe on GaAs and Si by the organometallic vapor phase epitaxial process at atmospheric pressure. Self-limiting growth at one monolayer was obtained over the temperature range from 250°C to 320°C, under a wide range of reactant pressure conditions. A study of growth mechanism indicates that DMCd decomposes into Cd on the surface and the Te precursors react catalytically on the Cd covered surface. We have used this ALE grown layer to improve the crystal quality and the morphology of conventionally grown CdTe on GaAs. Improvement in the crystal quality was also observed when ALE CdTe nucleation was carried out on Si pretreated with DETe at 420°C. Atomic layer epitaxy grown ZnTe was used to obtain (100) oriented CdTe on (100) silicon.     

Electrical and structural characterization of GaAs vertical-sidewall epilayers grown by atomic layer epitaxy

Electrical and structural measurements have been performed on novel test structures incorporatingp-type GaAs epilayers grown by organometallic vapor phase atomic layer epitaxy on the vertical sidewalls of semi-insulating GaAs rods formed by ion-beam-assisted etching. Preliminary results indicate that the vertical-sidewall epilayers have excellent crystal quality and sufficient electrical quality to support a sidewall-epitaxy device technology. Some examples of candidate electronic, electrooptic, and photonic devices for vertical-sidewall fabrication are FETs, resistors, waveguides, modulators, and quantum-wire and quantum-dot lasers.     

Atomic layer epitaxy of InP

In this work we will discuss the growth conditions for ALE of InP. Growth experiments were carried out in a LP-MOCVD system with a fast switch gas manifold. InP layers were deposited by pulsing TMIn and PH₃, using Argon as carrier gas. A self limiting growth rate at 1 ML/cycle has been obtained with a substrate temperature as low as 320-360° C. InP epitaxial layers were grown on GaAs and InP substrates, and on GaInAs(P) layers previously deposited by conventional MOCVD. Selective area epitaxy on InP using a Si₃N₄ mask was also demonstrated. Results of this study are very encouraging for hybrid MOCVD/ALE growth of In-based compounds.     

Monomolecular layer epitaxy of GaAs for ideal static induction transistor

An ideal static induction transistor (ISIT) structure was fabricated using molecular layer epitaxy (MLE). The doping method of MLE enabled us to achieve a sufficiently high level of doping for ISIT fabrication. In the fabrication process a low growth temperature was very important for the device structure, which requires very sharp dopant profiles. For the ISIT, two MLE processes, namely source–drain growth and gate regrowth, were required. The electrical characteristics of the source–drain were changed after heat treatment at a temperature higher than 480°C. The effect of the redistribution of dopants of the source–drain structure (n⁺⁺–i–p⁺⁺–i–n⁺) during gate regrowth was clearly shown by SIMS (secondary ion mass spectroscopy) measurements for various temperatures of heat treatment. As a result the doped Se diffused from the n⁺⁺ source region to the other layers and the doped Zn diffused from the p⁺⁺ layer to the i-layers. The source was a heavily Se-doped layer at the doping level of (2–3)×10¹⁹ cm⁻³ containing a larger amount of interstitial Se atoms in the lattice. The redistribution of Se from the heavily doped region was detectable even after heat treatment at 480°C for 30 min. For the p⁺⁺ layer the profile of the C-doped layer was stable even after heat treatment at 620°C for 30 min, but the profile of Zn changed markedly after heat treatment at 480°C for 30 min. In addition, the carbon-doped p⁺⁺ layer acted as a gettering layer for diffused interstitial Se from the source region. The driving force of the redistribution of dopants results in the electric field in the device structures. © 1997 John Wiley & Sons, Ltd.     

Atomic layer epitaxy of nitrogen-doped ZnSe

Atomic layer epitaxy of nitrogen-doped ZNSe was studied. The ZnSe films were grown on GaAs(00l) substrates at 250°C with a continuous flow of nitrogen and alternate supplies of zinc and selenium. The grown films were characterized by photoluminescence spectra at 4.2K, and it was found that nitrogen was incorporated as a shallow acceptor in the films. The Schottky diodes were prepared by evaporating gold on the nitrogen-doped films grown on p-type GaAs substrates. A rectifying characteristic that was consistent with the structure, assuming p-type conductivity of ZnSe, was observed. Capacitance-voltage measurement of the structure also indicated p-type conductivity of the films.     

Electrical properties and interfacial chemical environments of in situ atomic layer deposited Al2O3 on freshly molecular beam epitaxy grown GaAs

Interfacial chemical analyses and electrical characterization of in situ atomic layer deposited (ALD) Al₂O₃ on freshly molecular beam epitaxy (MBE) grown n- and p- GaAs (001) with a (4 × 6) surface reconstruction are performed. The capacitance-voltage (C-V) characteristics of as-deposited and 550 °C N₂ annealed samples are correlated with their corresponding X-ray photoelectron spectroscopy (XPS) interfacial analyses. The chemical bonding for the as-deposited ALD-Al₂O₃/n- and p-GaAs interface is similar, consisting of Ga₂O (Ga¹⁺) and As-As bonding (As⁰) without any detectable arsenic oxides or Ga₂O₃; the interfacial chemical environments remained unchanged after 550 °C N₂ annealing for 1hr. Both as-deposited and annealed p-GaAs metal-oxide-semiconductor capacitors (MOSCAPs) exhibit C-V characteristics with small frequency dispersion (<5%). In comparison, n-GaAs MOSCAPs shows much pronounced frequency dispersion than their p-counterparts.     

Growth rate reduction in self-limiting growth of doped GaAs by molecular layer epitaxy

Self-limiting growth of GaAs with doping by molecular layer epitaxy (MLE) has been studied using the intermittent supply of TEG, AsH₃, and a dopant precursor, Te(C₂H₅)₂ (diethyl-tellurium: DETe) for n-type growth on GaAs (0 0 1). The self-limiting monolayer growth is applicable at 265°C, however, the growth rate per cycle of doping decreased and saturated at about 0.4 monolayer with increasing doping concentration. To clarify the mechanism of growth with doping and to solve the problem of the growth rate reduction, a doping cycle followed by several cycles of undoped growth was performed. The growth rate reduction in the TEG–AsH₃ system is due to the electrical characteristics of the growing surface, namely, the exchange reaction of TEG is reduced with increasing doping concentration.     

Photoluminescence study of GaAs films on Si(100) grown by atomic hydrogen-assisted molecular beam epitaxy

Preliminary experimental results and analysis of photoluminescence (PL) measurements performed on GaAs heteroepitaxial films, which have been grown on Si(100) substrates by atomic hydrogen-assisted low-temperature molecular beam epitaxy technique have been presented and discussed. The results have also been compared with those obtained for GaAs homoepitaxial films. Furthermore, minority carrier lifetimes in n-GaAs on Si have been characterized by the PL decay method and an average lifetime of as high as 8.0 ns has been successfully obtained, which is the highest value ever reported to date.     

Reaction mechanisms of tertiarybutylarsine on GaAs (001) surfaces and its relevance to atomic layer epitaxy and chemical beam epitaxy

We explore the use of tertiarybutylarsine (TBAs) as an alternative arsine source in atomic layer epitaxy (ALE) of GaAs. X-ray photoelectron spectroscopy (XPS), reflection high energy electron diffraction (RHEED), and reflectance difference spectroscopy (RDS) are used to characterize the surface reactions of TBAs on GaAs (001) Ga-rich surfaces. At a substrate temperature of 320° C and an exposure level of 90 L of TBAs, AsH_x (x = 1 or 2) is thought to be the adsorbed arsenic species. As the substrate temperature increases, As-rich surfaces are readily obtained with improved RHEED 2 x 4 patterns. No carbon related species are observed throughout the TBAs exposure experiments between 320° C and 540° C. It is suggested that AsH_x is the adsorbed species after TBAs decomposes on surface Ga atom. Interactions between AsH_x pairs form arsenic atoms by H₂ release. RDS allows anin-situ real time study of TBAs on GaAs (001) Ga-rich surfaces. It is found that the RDS results are consistent with those obtained from XPS and RHEED investigations and can provide information on the rates of reactions and the extent of surface reconstruction simultaneously. Implications for the growth of GaAs by atomic layer epitaxy and chemical beam epitaxy using TBAs are discussed.     

RHEED and XPS observations of trimethylgallium adsorption on GaAs (001) surfaces—Relevance to atomic layer epitaxy

A series of experiments under UHV conditions have been performed to determine the surface reacted species and surface structure that results from trimethylgallium (TMGa) adsorption on a GaAs (001) As-stabilized surface. In these experiments, the conditions were chosen to simulate typical ALE growth conditions. Thus, the substrate temperature was varied between 320 and 530° and an admittance of 10⁻⁷ to 5 × 10⁻⁶ Torr of TMGa with exposure time of 5 to 15 sec were applied. X-ray photoelectron spectroscopy (XPS) was used to identify the chemical species on the surface after TMGa adsorption. The XPS intensity associated with the Ga 2p _3/2 level was used to monitor the quantity of adsorbed Ga and RHEED was used to monitor the surface structure. Below 440°, the Ga intensity was saturated at a level close to 1 ML and no definite Ga-stabilized 4 ×X RHEED pattern was observed. At 320° and an exposure of 200 L, a 2 × 4 As-stabilized RHEED pattern still existed, which suggests that the reaction between impinging TMGa and the (001) GaAs surface is very slow at this temperature. When the substrate temperature was between 440 and 530° exposure to greater than 6 L of TMGa resulted in saturation of surface Ga atoms to one monolayer (ML) and a successive change of surface reconstruction from 2×4 As-stabilized to 4 ×X (X = 1 or 2) Ga-stabilized surface. In all runs no carbon related species were observed within the XPS detection limit. This observation suggests that adsorption and decomposition of TMGa on As sites goes to completion very rapidly in this temperature range. From these observations we conclude that the self limiting mechanism in ALE occurs because of the differential chemisorption and decomposition rates of TMGa on As and Ga sites and that the dominant surface adsorbate is atomic Ga. This work is partially supported by the Office of Naval Research under contract No. N00014-84-K-0331 and Solar Energy Research Institute Subcontract No. XB-5-05009-3.     

Gallium arsenide and (alga)as devices prepared by Liquid-Phase epitaxy (Review Article)

Gallium arsenide and (AlGa)As devices and their preparative techniques based on liquid-phase epitaxy are reviewed. Included are discussions of dopants, growth apparatus and structures used in light emission, electron emission, photodetection, and microwave systems.     

Atomic layer epitaxy of CdTe-ZnTe and CdTe-MnTe Superlattices

CdTe-ZnTe superlattices (SLs) with a period ranging from 13 to 38Å have been grown by atomic layer epitaxy (ALE) on (001) GaAs-substrates. In a substrate temperature range between 270 and 290°C, the growth rate for both CdTe and ZnTe regulated itself to exactly 0.5 monolayers per reaction cycle, allowing the growth of very precisely tailored structures. For lower substrate temperatures, the growth rate raised to approximately 0.8 monolayers per cycle, but did not reach one monolayer per cycle before ZnTe started to grow polycrystalline. Using the ALE growth parameters for CdTe, SLs of CdTe and metastable cubic MnTe were prepared. The superlattices were characterized by high resolution x-ray diffraction and photoluminescence. A comparision of x-ray data and computer simulations, based on the dynamical theory of x-ray diffraction, show that the SLs exhibit excellent period constancy and very abrupt interfaces.     

新结构InGaP/GaAs/InGaP DHBT生长及特性研究

设计并生长了一种新的InGaP/GaAs/InGaP DHBT结构材料,采用在基区和集电区之间插入n+-InGaP插入层结构,以解决InGaP/GaAs/InGaP DHBT集电结导带尖峰的电子阻挡效应问题。采用气态源分子束外延(GSMBE)技术,通过优化生长条件,获得了高质量外延材料,成功地生长出带有n+-InGaP插入层结构的GaAs基InGaP/GaAs/InGaP DHBT结构材料。采用常规的湿法腐蚀工艺,研制出发射极面积为100μm×100μm的新型结构InGaP/GaAs/InGaP DHBT器件。直流特性测试的结果表明,所设计的集电结带有n+-InGaP插入层的InGaP/GaAs/InGaP DHBT器件开启电压约为0.15V,反向击穿电压达到16V,与传统的单异质结InGaP/GaAs HBT相比,反向击穿电压提高了一倍,能够满足低损耗、较高功率器件与电路制作的要求。     

Flow modulation epitaxy of indium gallium nitride

InGaN layers were grown on GaN films by flow modulation epitaxy (FME) using the precursors trimethylgallium, trimethylindium, and ammonia. The indium composition of the FME grown layers was generally lower than of films grown under the same conditions in the continuous growth mode, but which had been of poor optical quality. The indium incorporation efficiency increased with decreasing ammonia flush time, increasing ammonia flow during group-III injection, and increasing group-III precursor injection time. Films grown under optimized conditions showed intense band edge related luminescence at room temperature up to a wavelength of 465 nm. Atomic force microscopy investigations revealed a strong dependence of the surface morphology of the InGaN films on the growth mode.     

Novel fully self-aligned MESFET using source and drain regrown nonalloyed contacts by ALE

A new low temperature, nonalloyed, self-aligned FET process using regrowth technology on a patterned substrate has been demonstrated. A double 8-doped MESFET with regrown n⁺⁺ source and drain contact regions using atomic layer epitaxy (ALE) were fabricated and characterized. In this novel regrowth technique, a silicide gate was embedded by molybdenum and a side wall oxide to prevent any contamination or unwanted reaction during the ALE growth. Two main features associated with our process that makes it an attractive technology for more uniform device performance across a large area wafer are: a) the refractory gate/GaAs interface is not subjected to any high temperature process, and b) nonalloyed ohmic contacts are achieved without undesirable lateral diffusion of n⁺ regions caused by annealing of implanted source and drain. The preliminary unoptimized device results show a transconductance of 40 mS/mm for gate length of 0.65 μn.