G.R. Booker

The epitaxial growth of silicon and germanium films on (111) silicon surfaces using UHV sublimation and evaporation techniques

Si and Ge layers have been grown on (111) Si substrates by sublimation or evaporation in UHV. The substrate temperatures ranged from 750 to 1000°C, and the deposition rates up to 3 A sec-1. Substrates were either heated directly to the deposition temperature, or initially pre-heated at 1250 °C. Structural observations were made using optical microscopy, transmission electron microscopy and scanning electron microscopy. An attempt is made in the case of the Si/Si system to explain the results in a quantitative manner with the aid of nucleation theory.

Nature, origin and effect of dislocations in epitaxial semiconductor layers

Abstract The paper is concerned with the manner in which dislocations in Group 3–5 compound epitaxial layer structures are generated, propagate and interact with one another. The different types of epitaxial layer and dislocation behaviour are initially reviewed. The examination methods used are based on electron microscopy. The TEM is used in conjunction with plan-view, cross-section, and angle-lap specimens to determine the detailed nature and three-dimensional distribution of the dislocations. The SEM EBIC and CL methods are used with bulk specimens to obtain electrical and luminescent information. In particular, the latter methods give micrograph-type images showing dark spots and lines corresponding to individual dislocations, the contrast arising because of electrical carrier recombination taking place at the dislocations. These methods are used to investigate the dislocation behaviours occurring in a wide range of specimens including homo- and hetero-epitaxial layers, and embracing small, medium and large mismatches. An attempt is made to obtain quantitative data concerning the processes occurring. The work has provided a better understanding in many instances, and sometimes allowed the occurrence of the dislocations to be better controlled. An example is given of the application of the results to the improvement in the quality of a GaAs transmission photocathode device-type structure.

Selective and Non-Planar Epitaxy of lnP, GalnAs and GalnAsP Using Low Pressure MOCVD

Abstract Selective area and non-planar MOCVD of InP, GaInAs, and GaInAsP can radically modify the properties of these alloys relative to planar “whole wafer” epitaxy. This paper outlines qualitative and quantitative studies aimed at understanding the various, often interrelated, effects and indicates their significance to the fabrication of integrated devices.

Growth of InAs/GaSb strained layer superlattices. I

Abstract InAs/GaSb strained layer superlattices (SLSs) have been grown by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. Whilst long period SLSs have been successfully grown by this technique, the growth of short period structures is adversely affected by step-bunching. By growing the SLSs faster and cooler, good periodicity was achieved as measured by Raman spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) in SLSs with bilayer (GaSb + InAs) thicknesses as thin as 50 A. We have also detected the InSb-like and GaAs-like interface modes from room temperature Raman measurements for the first time in MOVPE grown samples. The most promising samples have been assessed by FIR photoconductivity at 4.2 K and show bandgaps (dependent on the bilayer thickness) between 5 and 20 μm.

Growth of InAsGaSb strained layer superlattices. II

Abstract InAs GaSb strained layer superlattices (SLSs) have been grown by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. Initially the interfaces of the SLS have been biased towards pairs of GaAs or InSb using three different gas switching sequences. Room temperature Raman optical modes show that growing the interfaces using an ALE (atomic layer epitaxy) like switching sequence gives interfaces of very high quality probably near the optimum, which is a monolayer, Growing with other switching sequences leads to one of the interfaces being non-uniform. By growing samples with alternating (InSb,GaAs or GaAs,InSb) pairs of interfaces it is possible to unambiguously assign this non-uniformity to one of the two possible interfaces for the first time. Furthermore, the influence of the band overlap on interface type has been studied using optimised SLSs in the semimetallic regime.

Improved materials for MOVPE growth of GaSb and InSb

Some factors affecting the MOVPE growth of GaSb and InSb and structures based on these materials and their alloys are investigated. Trimethylantimony (TMSb) and tertiarybutyldimethylantimony (TBDMSb) have been synthesized and assessed by growing bulk layers of GaSb and InSb. The use of TBDMSb has allowed the growth of InSb at 400 degrees C as compared with 450 degrees C using TMSb. all the alkyls used have had their pyrolysis kinetics determined under real growth conditions using in situ ultraviolet spectroscopy. A thorough study of the initial nucleation of GaSb onto GaAs substrates has been performed using atomic force microscopy (AFM), TEM (cross-sectional and plan view) and quasi-elastic light scattering (QLS). Bulk layers of GaSb have been grown using optimized and non-optimized buffer layers to assess the effect on optical, structural and electrical properties of the grown layers.

SEM and TEM studies of defects in Si-doped GaAs substrate material before and after Zn diffusion

Si‐doped GaAs slices after Zn diffusion exhibited a marked decrease in luminous efficiency and a large increase in p‐n junction depth when the initial carrier concentration due to the Si was > 3·5 times 1024 m−3. SEM studies using the CL and EBIC methods, and TEM examinations using plan‐view and cross‐section specimens, showed that these behaviours were associated with high densities of structural defects, interpreted as Zn precipitation. Reasons for these behaviours in terms of nucleation behaviour and diffusion mechanisms are suggested.

Electron Microscope Studies Of Vpe Gainas Layer Structures Suitable For Use As Infrared Leds

Electron microscope investigations have been carried out on vapour grown (100) GaAs/GaInAs structures designed for use as infrared emitters of wavelength 1·06 μm. The structures consist of a GaAs substrate, a graded layer in which the indium concentration is increased from zero to 17 atomic %, and a constant composition Ga0·83In0·17As layer which contains a p‐n junction. X‐ray microprobe analysis of cross‐sections of the slices established the uniformity of the grading. TEM analysis showed a dense and extensive asymmetric network of misfit dislocations (1 × 1012 m−2 (108 cm−2)) in the graded layer, threading dislocations and other anomalous contrast features extending from the graded layer through the p‐n junction to the surface (local densities of 1 × 1011–1 × 1012 m−2 (107–108 cm−2)), and a planar network of dislocations just below the surface (spacing 0·2–2 μm). SEM EBIC and CL studies of the layer above the junction revealed dark spots, and a cross‐grid of dark lines, which could be correlated with the threading defects, and the dislocation network just below the surface, respectively. The SEM results showed that these defects had a deleterious effect on the luminescent and electrical properties of the material in the vicinity of the p‐n junction, and would therefore impair the performance of devices made from these layer structures.

Interface abruptness in LPE grown (CdHg) Te layers on CdTe substrates

The abruptness of interfaces between liquid phase epitaxial grown layers of CdxHg1 - xTe and the CdTe(111) substrates on which they are grown has been studied by four techniques used for compositional profiling. These are: (i) energy-dispersive electron probe micro-analysis (ED-EPMA) at 5 and 25 kV; (ii) wavelenght-dispersive electron probe micro-analysis (WD-EPMA) at 15 kV; (iii) secondary-ion mass spectrometry SIMS) using a 12.5 kV O+2 primary beam and (iv) backscattered electron analysis analysis (BSE) in the scanning electron microscope at 15 and 35 kV. These techniques have been applied to specimens from a single epitaxial layer. The distances as for the 10% to 90% compositional transition were measured, and values varying from 2 mum for ED-EPMA to 0.23 mum for BSE analysis were found. These results indicate the misleading measurements of interface abruptness that can be obtained on epitaxial specimens if consideration is not paid to the spatial resolution of the measurement technique and the topographic structure of the specimen. The potential of the BSE technique for high resolution compositional profiling and two-dimensional mapping will be discussed and the causes of the erroneous results obtained with the other techniques will be highlighted. The fact that the interface abruptness in this LPE specimen (≤ 0.23 mum) is a factor of ten less than conventionally measured for LPE (CdHg)Te layers has important consequences for the use of LPE for the growth of multilayer IR detector structures.

Comparison of surface polishing techniques used for InP wafers

Abstract InP wafers prepared using different polishing and mounting methods were compared by Makyoh topography, which is capable of detecting extremely small surface height variations. In some wafers a cellular surface ridge structure due to uneven mounting wax distribution was observed. It is shown that the ridge structure can be completely eliminated by the optimisation of the wafer mounting procedure or by the use of a “free floating” double sided polishing technique.