An investigation of the annealing of LEC semi-insulating GaAS
An investigation of the annealing of LEC semi-insulating GaAS
The objective of this study was to investigate the effect of annealing LEC semi-insulating GaAs under controlled annealing conditions of varying arsenic partial pressures, times and temperatures. This work was carried out with the aim of furthering the understanding of the behaviour of point defects in this material during annealing. This thesis first describes some of the physical and growth characteristics of GaAs, followed by a review of point defects, the semi-insulating behaviour and role of dislocations in GaAs. The Bond Method of precise lattice parameter measurement, and etching techniques were used to characterise the behaviour of GaAs when annealed at 950oC and 1050oC. Arsenic partial pressures of 1, 2.5 and 4 atmospheres and annealing times of 5 and 25 hours were used during this investigation. The lattice parameters of annealed samples were compared to those prior to annealing with one atmosphere arsenic pressure, resulting in a mean lattice parameter expansion of about 3.75 ppm. The higher arsenic pressure of anneal gave rise to mean lattice parameter contractions of between 1 and 2 ppm. The difference in lattice parameter before and after annealing was taken as a measure of the concentration of point defects involved during annealing. These changes were shown to be temperature and pressure dependent. It is postulated from experimental data obtained during this investigation that two or more defect reactions compete for dominance at 950oC. At an arsenic partial pressure of one atmosphere during annealing the dominant defect reaction is suggested as arsenic vacancy formation at a concentration of about 2.3 x 1017 cm-3, whilst arsenic partial pressures of 2.5 atmospheres or greater gallium divacancies are formed at concentrations of approximately 1017 cm-3. The formation energy of the gallium divacancy has been estimated as 0.46 eV, with the maximum diffusivity of this defect given as 4 x 10-11 cm2 s-1. When annealed samples are held at 26oC after high temperature annealing, the lattice parameter changes with time. This observation has previously been noted, although the changes were of greater magnitude than those of this investigation. The observed change has been ascribed to arsenic vacancy coalescence in samples annealed under a one atmosphere arsenic partial pressure, and to gallium divacancy coalescence at 2.5 atmosphere or higher arsenic partial pressure of anneal. (D82628)
University of Southampton
1987
Stoakes, Rosemarie Clare
(1987)
An investigation of the annealing of LEC semi-insulating GaAS.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The objective of this study was to investigate the effect of annealing LEC semi-insulating GaAs under controlled annealing conditions of varying arsenic partial pressures, times and temperatures. This work was carried out with the aim of furthering the understanding of the behaviour of point defects in this material during annealing. This thesis first describes some of the physical and growth characteristics of GaAs, followed by a review of point defects, the semi-insulating behaviour and role of dislocations in GaAs. The Bond Method of precise lattice parameter measurement, and etching techniques were used to characterise the behaviour of GaAs when annealed at 950oC and 1050oC. Arsenic partial pressures of 1, 2.5 and 4 atmospheres and annealing times of 5 and 25 hours were used during this investigation. The lattice parameters of annealed samples were compared to those prior to annealing with one atmosphere arsenic pressure, resulting in a mean lattice parameter expansion of about 3.75 ppm. The higher arsenic pressure of anneal gave rise to mean lattice parameter contractions of between 1 and 2 ppm. The difference in lattice parameter before and after annealing was taken as a measure of the concentration of point defects involved during annealing. These changes were shown to be temperature and pressure dependent. It is postulated from experimental data obtained during this investigation that two or more defect reactions compete for dominance at 950oC. At an arsenic partial pressure of one atmosphere during annealing the dominant defect reaction is suggested as arsenic vacancy formation at a concentration of about 2.3 x 1017 cm-3, whilst arsenic partial pressures of 2.5 atmospheres or greater gallium divacancies are formed at concentrations of approximately 1017 cm-3. The formation energy of the gallium divacancy has been estimated as 0.46 eV, with the maximum diffusivity of this defect given as 4 x 10-11 cm2 s-1. When annealed samples are held at 26oC after high temperature annealing, the lattice parameter changes with time. This observation has previously been noted, although the changes were of greater magnitude than those of this investigation. The observed change has been ascribed to arsenic vacancy coalescence in samples annealed under a one atmosphere arsenic partial pressure, and to gallium divacancy coalescence at 2.5 atmosphere or higher arsenic partial pressure of anneal. (D82628)
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Published date: 1987
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Local EPrints ID: 461903
URI: http://eprints.soton.ac.uk/id/eprint/461903
PURE UUID: 1afd911e-06c9-44da-9e02-8419ffc7316f
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Date deposited: 04 Jul 2022 18:58
Last modified: 04 Jul 2022 18:58
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Author:
Rosemarie Clare Stoakes
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