C. R. Whitehouse

Modulated-beam mass spectrometry studies of the MOMBE growth of (100) GaAs and In0.1Ga0.9As

Abstract Modulated-beam mass spectrometry has been used for the first time to study the MOMBE growth of (100) GaAs and In 0.1 Ga 0.9 As using appropriate combinations of triethyl gallium, triethyl indium and arsenic tetramer sources. The GaAs MOMBE growth process has been monitored as a systematic function of substrate temperature, V : III flux-ratio and growth rate. These experiments indicate that rapid thermal decomposition of triethyl gallium takes place with increasing substrate temperature (80–350°C) to generate an increasing concentration of desorbing diethyl gallium. For substrate temperatures greater than 350°C, progressively increasing thermal decomposition of the diethyl gallium occurs at the substrate surface, and GaAs growth commences. Three specific subsequent growth regions are then identified as a function of increasing substrate temperature. The data obtained as a function of the different growth variables is then used to explain previously reported GaAs MOMBE growth rate results, and implications for the existing models of MOMBE growth processes are described. Finally, preliminary modulated-beam mass spectrometry data obtained during the MOMBE growth of In 0.1 Ga 0.9 As is described and correlated with previously reported In x Ga 1 − x As MOMBE growth studies.

Heteroepitaxial growth of InSb on (100)GaAs using molecular beam epitaxy

Molecular beam epitaxy has been used to grow thin (0.5 μm<t<10 μm) InSb epilayers on (100) GaAs substrates. Reflection high‐energy electron diffraction studies indicate that the early stages of layer growth involve three‐dimensional nucleation and the formation of a nonpseudomorphic structure. High‐resolution electron microscopy studies of the interface are reported for the first time and directly confirm that the large lattice mismatch (14.6% at room temperature) is accommodated by the generation of misfit dislocations. Nevertheless, the structural quality of the InSb is observed to improve dramatically with increasing thickness. Detailed secondary‐ion mass spectrometry measurements also demonstrate that there is no large‐scale interdiffusion of constituent elements at the interface. Finally, electrical measurements show the InSb to be p type and comparable with homoepitaxial material.

Real-time laser-light scattering studies of surface topography development during GaAs MBE growth

Abstract In-situ laser light scattering is shown to yield valuable real-time information on the development of surface micro-topography during GaAs MBE growth. In-vacuo oxide desorption results in a large increase in scattered light intensity. Ex-situ atomic force microscopy has indicated the formation of a high density (>10 9 cm -2 ) of surface pits, attributed to localized GaAs consumption. Subsequent GaAs homoepitaxial growth (at 600°C) results in the development of an anisotropic ridged topography (ridge axes parallel to [110] with ridge dimensions increasing with epilayer thickness (peak-valley ≤ 12 nm for a 2.0 μm thick epilayer). Post growth in-vacuo annealing generates relatively flat surfaces, dominated by misorientation steps. For a 1 μm thick epilayer, annealing has a long time constant ( > 30 min at 600°C).

Surface topography changes during the growth of GaAs by molecular beam epitaxy

Changes in surface roughness taking place during (001) GaAs molecular beam epitaxy growth have been studied in situ using laser light scattering and ex situ using atomic force microscopy (AFM). Substantial increases in light scattering are found to occur firstly during oxide thermal desorption, associated with surface pit formation, and secondly during continued layer growth, due to the buildup of atomic step arrays. Monolayer height GaAs steps are readily resolved using AFM in air.

An MBE route towards CdTe/InSb superlattices

As part of a program aimed at the growth of CdTe/InSb superlattices, a systematic study has been made of the MBE growth of heteroepitaxial CdTe layers on (001)InSb using substrate temperatures, Ts, significantly higher than have been previously reported. Using a modified two‐step growth technique, high quality layers have been successfully grown at temperatures as high as 310 °C with no evidence of either preferential Cd loss or CdTe/InSb interdiffusion. The new growth technique is described and cross‐sectional TEM and SIMS data from the grown layers is presented.

Chemical and electronic structure of InSb‐CdTe interfaces

The microscopic interactions at heterojunctions formed between cleaned surfaces of InSb and CdTe have been investigated by low‐energy electron diffraction and soft x‐ray photoelectron spectroscopy. Layers of CdTe have been deposited on 1×1 (110) cleaved InSb and on c(2×8) (100) sputter cleaned and annealed surfaces, for various substrate temperatures. The valence‐band offset has been measured and compared with theoretical predictions for layers deposited on room‐temperature substrates. For layers deposited onto substrates at elevated temperatures typical of those employed in molecular beam epitaxial growth, the interface is complex and consists of a region rich in indium and tellurium, presumed to be indium telluride. The thickness of this layer is temperature dependent and may be several tens of angstroms.

Growth mechanism studies in CBE/MOMBE

Abstract The ultra-high vacuum environment used for chemical beam epitaxy (CBE) and metalorganic molecular beam epitaxy (MOMBE) provides the important capability to perform detailed in-situ studies of the reaction processes involved. Despite the relative immaturity of both the CBE and MOMBE growth techniques, significant advances in this understanding are therefore already being made. The present paper reviews the current knowledge of CBE/MOMBE reaction processes and discusses implications of the relevant experimental observations in relation to the early theoretical models of CBE growth. The authors then propose specific topics which require further investigation if the full potential of CBE and MOMBE is to be exploited.

Material‐dependent amorphization and epitaxial crystallization in ion‐implanted AlAs/GaAs layer structures

When AlAs/GaAs layer samples are subjected to Ar+ ion bombardment at liquid‐nitrogen temperature, it is shown that very different damage structures are produced in the two materials. While the GaAs is relatively easily amorphized, the AlAs is quite resistant to damage accumulation and remains crystalline for the ion doses employed in these investigations. Epitaxial regrowth of buried amorphous GaAs layers of thicknesses up to 150 nm can be induced by rapid thermal annealing. It is demonstrated that differences in the initial damage state have a strong influence upon the nature of lattice defects produced by annealing.

Ambient temperature diodes and field-effect transistors in InSb/In1-xAlxSb

InSb and related narrow‐gap alloys have many potential applications in addition to the conventional one of infrared detection, provided that ambient temperature operation can be achieved. We report experimental results on multilayer InSb/In1−xAlxSb structures utilizing minority‐carrier exclusion and extraction. At room temperature, diodes have R0A values several orders higher than homostructure InSb devices. Negative differential resistance associated with Auger suppression is observed under reverse bias. Enhancement‐mode metal‐insulator‐semiconductor field‐effect transistors have near classical output characteristics at 294 K, with a typical transconductance of 34 mS/mm and dynamic range of 23 dB.

Tri‐isopropyl gallium: A very promising precursor for chemical beam epitaxy

The first reported use of tri‐isopropyl gallium (TiPGa) in chemical beam epitaxy (CBE) is described. Hall measurements performed on the resulting undoped GaAs epitaxial layers indicate an order of magnitude reduction in unintentional carbon impurity levels compared to structures grown under comparable conditions using the standard CBE precursor, triethyl gallium. 2 K photoluminescence spectra match those recorded elsewhere from state‐of‐the‐art high purity GaAs material grown by molecular beam epitaxy, and 77 K Hall measurements on intentionally n‐type doped GaAs layers confirm residual acceptor levels in the low 1014 cm−3 range. The early data obtained already provide a clear indication of the important potential of TiPGa as an improved precursor for the CBE growth of Ga‐containing III–V materials.