R.W. Freer

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.

New metalorganic gallium precursors for the growth of GaAs and AlGaAs by CBE

Abstract The use of triethylgallium (TEGa) for the CBE growth of GaAs and AlGaAs leads to very significant reductions in unintentional carbon incorporation compared to corresponding layers grown using trimethylgallium (TMGa). However, in a continuing effort to generate even further reductions in impurity levels, the present paper provides the first reported comparison of the tri-isopropylgallium (TIPGa) and tri-tertiarybutylgallium (TTBGa) precursors for CBE growth applications. The use of TTBGa is found to lead to unacceptably low GaAs growth rates, an effect which is attributed to a steric influence on the chemisorption process. In contrast, the TIPGa-grown GaAs layers exhibit very important improvements in electrical and optical properties compared to corresponding TEGa-grown material. Results of initial AlGaAs growth experiments performed using TIPGa are also presented.

Mechanistic studies of the CBE growth of (100) GaAs using the new precursor tri-isopropylgallium

Abstract Modulated-beam mass spectrometry and temperature programmed desorption have for the first time been used to investigate the decomposition of tri-isopropyl gallium (TIPGa) on the (100) GaAs surface. Significant differences in the substrate temperature dependence of the GaAs growth rate have been observed between growth using TIPGa and the standard CBE precursor triethylgallium (TEGa). These differences are explained in terms of the balance between desorption and decomposition of adsorbed di-isopropyl gallium radicals shifting in favour of desorption.

Improved GaAs/Ga1−xAlxAs chemical beam epitaxy using triisopropylgallium

Abstract Very recent studies performed by the authors have shown that the use of the new triisopropylgallium (TiPGa) precursor leads to an important order-of-magnitude reduction in unintentional carbon impurity levels in GaAs layers grown by chemical beam epitaxy (CBE), when compared with layers grown using triethylgallium (TEGa). The present paper provides additional GaAs growth data, particularly relating to the layer growth rate dependence on substrate temperature, and then describes the first reported use of TiPGa for Ga 1−x Al x As CBE growth. When used in combination with alane trimethylamine, the TiPGa precursor again leads to significant reductions in unintentionally incorporated carbon impurity levels in the resulting Ga 0.7 Al 0.3 As CBE layers, compared with corresponding TEGa-grown material. Initial GaAs/Ga 1-x Al x As two-dimensional electron gas (2DEG) structures have also been grown and have already exhibited 77K and 4 K 2DEG mobility values of 62 000 cm 2 V −1 s −1 and 104 000 cm 2 V −1 s −1 respectively.

Chemical beam epitaxial growth of high optical quality AlGaAs — the influence of precursor purity on material properties

Abstract The influence of source precursor purity on the quality of resulting chemical beam epitaxy (CBE) grown AlGaAs epilayers has been investigated. A close correlation has been established between the presence of trace quantities of diethyl ether in a precursor and consequent oxygen contamination of AlGaAs. Careful selection and purification of the precursors to reduce ether contamination has generated significant improvements in both the optical and electrical properties of CBE-grown AlGaAs, such that it is now directly comparable with high quality molecular beam epitaxy (MBE) and metalorganic vapour phase epitaxy (MOVPE) grown material.

Increasing the range of growth temperatures available for GaAs selective area growth using triisopropylgallium and arsine

This paper reports the first assessment of triisopropylgallium (TIPGa) for the selective area growth of GaAs using chemical beam epitaxy. Modulated beam mass spectrometry has been used to study the decomposition of TIPGa on oxides of silicon and GaAs, with both pre-cracked arsine and tris(dimethylamino)arsenic (TDMAAs) as the group V source. Experiments have been performed as a systematic function of growth temperature, both with and without the group V flux, and a comparison made with the use of triethylgallium (TEGa) in place of TIPGa. Using pre-cracked arsine as the group V source, we have demonstrated that TIPGa does not decompose on a silicon oxide surface for all growth temperatures above 450°C, whereas temperatures over 560°C are required to achieve total selectivity when using TEGa as the group III source. Studies using TIPGa and TDMAAs also demonstrate selectivity across a wide temperature range.

Chemical‐beam‐epitaxy growth of indium‐containing III–V compounds using triisopropylindium

Triisopropyl indium (TIPIn) has been investigated as an alternative to trimethyl indium for use in chemical‐beam epitaxy (CBE). In previous CBE studies of GaAs/AlGaAs growth, the replacement of methyl‐containing precursors with ethyl‐ and isopropyl‐containing precursors has been shown both to widen the substrate temperature window available for growth, and also to reduce unintentional carbon incorporation in the grown layers. In the present study of (100)InxGa1−xAs (0≤x≤0.1) growth using the new TIPIn source, in situ modulated‐beam mass spectrometry studies have demonstrated a similar, and technologically very important, widening of the substrate temperature window. Furthermore, use of the new precursor combination, TIPIn and triisopropyl gallium, is also shown to generate state‐of‐the‐art InGaAs material with electrical and optical properties directly comparable to corresponding material grown using molecular‐beam epitaxy.

Advances in the understanding of chemical beam epitaxy growth mechanisms

Abstract The advanced epitaxial growth capabilities provided by chemical beam epitaxy (CBE) have generated significant interest in the technique for the growth of next-generation device structures. Furthermore, this growth potential is complemented by the control and characterization facilities provided by the ultra-high vacuum environment. Considerable insight is therefore being gained into the detailed growth mechanisms involved in CBE, and particularly the decomposition of the precursor sources. This current paper reviews the current understanding of the CBE-growth process, and highlights some important recent developments.