Development of MOVPE-grown InAsSb for barrier diode applications
- Authors: Dobson, Stephen R
- Date: 2020
- Subjects: Gallium arsenide semiconductors , Electronics
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/49071 , vital:41598
- Description: In this study, layers of GaSb, InAs and InAsSb are grown by metalorganic vapour phase epitaxy and characterised. Growth is conducted using the precursors of trimethylgallium, trimethylindium, trimethylantimony and tertiarybutylarsine. Focus is then placed on the characterisation of the materials, carried out by the techniques of X-ray diffraction, photoluminescence spectroscopy, Hall measurements and photocurrent spectroscopy. It is observed that V/III ratio plays a vital role in the growth of the GaSb and InAsSb layers. Epilayers of GaSb showed best crystalline quality when a V/III ratio of 1.2 was used at a growth temperature of 600 °C and a cell pressure of 600 Torr. Resultant Hall measurements indicated p-type GaSb. The Hall carrier concentrations of the p-type GaSb samples were analyzed considering electrical neutrality conditions and found to be highly compensated with evidence of band impurity conduction at low measurement temperatures. Both the donor and acceptor concentrations were determined to be of the order of 1016 cm−3 for all samples. For low temperature (< 150 K) a monovalent acceptor concentration is calculated to have an activation energy at approximately 20 meV. At high temperature (> 150 K) a divalent acceptor is extracted with an activation energy varying between samples based on compensation in a range of 90 meV to 70 meV. Photoluminescence measurements show four peaks with recombination mechanisms linked to the native acceptor identified in literature as either the gallium antisite and/or vacant gallium site. A fifth peak observed is attributed to the longitudinal phonon of the native acceptor. InAs and InAsSb epilayer are all grown at a temperature of 600 °C and cell pressure of 600 Torr. InAs is grown at a V/III ratio of 9.5 on GaAs substrate. Photoluminescence of the InAs layer shows two distinct peaks, one of which is an extrinsic band to band recombination. The other is attributed to free electron to acceptor or a donor-acceptor pair transition. An additional weak peak is also observed which is assigned to the longitudinal phonon of the band to band. InAsSb growth was conducted under a range of V/III ratios of 4.8 to 5, with a vapour phase composition of 0.4 to 0.435. Structural analysis via X-ray diffraction showed a 6 % to 12 % solid antimony content. Photoluminescence exhibited a single broad peak for all samples, with extended band tails. Temperature and power dependant analysis of luminescence indicated a convolution of extrinsic band to tail and band to band recombinations. Hall measurements indicated the InAsSb was n-type material with an apparent measured maximum mobility at 120 K of 9.5 × 103 cm2/V.s. and a room temperature apparent mobility of 7.5 × 103 cm2/V.s. Analysis of hall results using a two-layer model calculated a true bulk mobility of the epilayer at room temperature with an increased value of 15.4 × 103 cm2/V.s. The two-layer model details the effects of the surface conduction. From photoconductivity measurements and further analysis a resultant effective lifetime, at room temperature, was found to be on same order of magnitude as that of InAs materials. Application of a single Einstein oscillator extrapolated 0 K energy gaps for two samples of solid Sb contents of 6 % and 12 %, of 354 meV and 332 meV, respectively. Finally consideration was given to the growth of aluminium containing compounds, particularly AlGaSb. Multiple phases were observed under scanning electron microscope showing growth of GaSb regions surrounded by amorphous solid aluminium and/or aluminium oxide phases. The failure of the aluminium to incorporate into the desired crystal structure is speculated to be due to impure precursor introducing oxygen into the films. Additionally, the effectiveness of the gallium precursor compared to the aluminium precursor in helping the removal of the methyl groups at the growth surface, could also promote a preference for GaSb growth.
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- Date Issued: 2020
On the electrical characterisation of bulk and epitaxial n-type Te doped GaSb
- Authors: Murape, Davison Munyaradzi
- Date: 2014
- Subjects: Gallium arsenide semiconductors , Electronics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10554 , http://hdl.handle.net/10948/d1020763
- Description: Since the development of the transistor in the Bell Telephone Laboratories in 1948 [78], the semiconductor industry has transformed the world we live in. It is difficult to picture a world without the modern day cutting edge technology. Imagine performing every day functions without “trivial” devices such as computers, cell phones or microwave ovens. The ability to tailor the band gaps of various binary, ternary and quaternary semiconductor systems has opened up a whole new spectrum of potential purpose designed devices [27]. This thesis focuses on the electronic properties of gallium (III) antimonide (V). The antimonides, in general, have the smallest band gap and highest electron mobility of the III-V compound semiconductors and are well suited for long wavelength emission and detection as well as high frequency switching device applications. Furthermore, III-V ternaries and quaternaries, such as (AlGaIn)(AsSb), lattice matched to gallium antimonide (GaSb) are considered serious competitors for HgCdTe and PbSe in long-wavelength infrared (LWIR) and very long-wavelength infrared (VLWIR) technology [4, 10, 11]. Epitaxial material systems based on GaSb are suitable for a wide range of applications such as missile and surveillance systems and a host of other military and civil applications. In addition, an assortment of devices on InAs, GaSb, and AlSb, including resonant tunnelling devices, infrared detectors and mid-infrared semiconductor lasers have been demonstrated [14, 15]. Furthermore, antimonide based devices could potentially reduce optical fibre power loss by a few orders of magnitude, as their implementation can lead to use of non-silica based optical fibres that minimise Raleigh scatter related power loss [8]. GaSb related technology faces a number of challenges. A significant amount of effort is required to exploit the potential it offers. GaSb oxidises readily in the ambient, resulting in the formation of a native oxide layer as well as deposits of elemental antimony (Sb) at the oxide/substrate interface therefore it has poor surface electronic properties resulting from high surface state densities[4, 17, 18]. As grown GaSb is characterised by a high density of surface states of which many are classified as non-radiative (Auger) recombination centres. The elemental Sb layer constitutes an unwanted conduction path parallel to the active surface region [17]. The potential that GaSb and GaSb-based strained layer superlattices offer as successors to the current generation of LWIR and VLWIR optoelectronic materials has therefore been largely impeded [4]. Furthermore, processing steps in device fabrication leads to an unintentionally damaged GaSb surface exacerbating the situation. Any efforts to engineer devices of superior quality on GaSb have to address these and more material specific problems [19]. This study attempts to contribute towards an improved understanding of the structural and electrical properties of the near surface region of Te-doped bulk (100) and MOVPE grown epitaxial Te doped n- GaSb. The main focus of this study is to develop means to de-oxidise and stabilize the highly reactive GaSb surface and to develop diode structures to demonstrate the improved interface characteristics and use related current–voltage (I-V) measurements to quantify the surface state density before and after treatment. These devices were also used to probe the near surface region for electrically active deep level defects that often act as non-radiative recombination centers. Au, Pd and Al were used as metals to establish a metal semiconductor barrier and subsequent depletion region. Sulphur based chemicals, ([(NH4)2S / (NH4)2SO4] + S), not previously reported for the treatment of (100) n-GaSb surfaces, and the commonly used passivants Na2S:9H2O and (NH4)2S were compared by assessing the electrical and structural properties both before and after treatment. The effect of treatment on the electrical response of the material was determined using current-voltage, capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements, while the surface morphology and composition were studied by SEM, AES and XPS.
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- Date Issued: 2014