M. Houlton

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.

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.

Selective area two-dimensional electron gas structures and in situ ohmic contacts patterned by focused ion beam doping during molecular beam epitaxial growth

Abstract For the first time, the technique of low energy focused ion beam (FIB) doping during molecular beam epitaxial (MBE) growth has been used to grow GaAs/AlGaAs based structures with three-dimensionally patterned doping profiles. Two applications are described. Selective area Sn ion doped two-dimensional electron gas (2DEG) structures were grown with a 1.2 K mobility of 200,000 cm 2 V -1 s -1 at a carrier concentration of 1×10 11 cm -2 . Further, selective area highly doped regions were patterned in situ to form low temperature, low resistance ohmic contacts to the 2DEG of conventional HEMT structures doped with a thermal Si source. The effects of Sn diffusion and ion beam damage were investigated in these structures.

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.

Dopant patterning of MBE GaAs during growth by very low energy focussed tin ion beam deposition

Abstract For the first time a focussed ion beam has been used to successfully dope MBE GaAs during growth. GaAs with a mobility of 73 000 cm2 V−1 s−1 at a carrier concentration of 1 × 1014 cm−3 has been attained which is the highest mobility MBE GaAs achieved by the technique of ionised beam doping. The use of a tin focussed ion beam as an MBE dopant source has also allowed the three-dimensional patterning of the dopant concentration in GaAs, for the first time. The focussed ion beam apparatus did not interfere with or affect the conventional MBE growth of GaAs and AlGaAs in the chamber.

Multilayer InSb diodes grown by molecular beam epitaxy for near-ambient temperature operation

InSb and related ternary alloys have many potential applications in addition to the conventional one of infrared detection provided that near ambient temperature operation can be achieved. The growth by MBE of n-type and p-type InSb has been established using silicon and beryllium dopants respectively. Multilayer diode structures have been studied up to 300K in order to determine carrier generation mechanisms and examine concepts for ambient temperature operation.

Effect of ion energy on Sn donor activation and defect production in molecular beam epitaxy GaAs doped with Sn ions during growth

The production of electrically active defect centers in molecular beam epitaxy (MBE) GaAs irradiated with low energy (50–500 eV) Sn ions during growth has been investigated as a function of ion energy. GaAs was doped n type during growth with a specially designed Sn focused ion beam column mounted on a MBE growth chamber. The 77 and 300 K Hall mobility and carrier concentration of the GaAs depended strongly on the ion energy, thus providing a sensitive measure of the concentration of ion‐induced acceptorlike defect centers. The material was found to be nonconducting for ion energies greater than 200 eV, while a systematic decrease in the acceptor concentration, and consequent increase in the mobility, was observed as the ion energy was decreased below this value. A peak mobility of 90 000 cm2 V−1 s−1 at a carrier concentration of 1×1014 cm−3 was achieved (at 60 K) which is in excess of that obtained in other reports of ion‐doped GaAs. A similar dependence on ion energy was found in the 4.2 K photoluminesc...

Characterization of alloy composition in Ga1-xAlxAs/GaAs structures: comparison of photovoltage, X-ray, SIMS and RHEED techniques

Abstract A comparative study of techniques for the characterization of alloy composition in Ga 1- x Al x As/GaAs single and multilayer structures has been carried out. Good agreement ( x ± 0.015) is demonstrated between double-crystal X-ray diffraction and photovoltage spectroscopy measurements using the generally accepted calibration of Casey and Panish. A slightly modified form of the band gap versus composition curve is presented which further improves the agreement to x ±0.005. Profiling conditions achieving linear SIMS Al profiles are reported, yielding compositions in agreement with PVS and X-ray within x +-0.01 (when calibrated at a single composition). A systematic discrepancy between results from the above techniques and in-situ RHEED oscillation measurements is reported.

Low-energy focused ion beam doping during molecular beam epitaxial growth for the fabrication of three-dimensional devices : the effect of dopant surface segregation

An extreme example of surface segregation is found in Sn-doped GaAs grown by molecular beam epitaxy (MBE). Abrupt changes in the doping profile are not possible, instead the dopant concentration decreases exponentially towards the wafer surface from the point at which doping was terminated. In this work it is shown that segregation can be suppressed by implanting the Sn from a very-low-energy (50 to 300 eV) ion beam during growth. The effect of ion implantation energy is studied using secondary ion mass spectroscopy (SIMS) to measure the depth profile of the implanted Sn. It is found that the level of incorporation can be increased by up to a factor of eight using a 300 eV ion energy.