P.A. Lane

Growth mechanism studies in CBE/MOMBE

Abstract The ultra-high vacuum environment used for chemical beam epitaxy (CBE) and metalorganic molecular beam epitaxy (MOMBE) provides the important capability to perform detailed in-situ studies of the reaction processes involved. Despite the relative immaturity of both the CBE and MOMBE growth techniques, significant advances in this understanding are therefore already being made. The present paper reviews the current knowledge of CBE/MOMBE reaction processes and discusses implications of the relevant experimental observations in relation to the early theoretical models of CBE growth. The authors then propose specific topics which require further investigation if the full potential of CBE and MOMBE is to be exploited.

Efficiency measurement of GaN-based quantum well and light-emitting diode structures grown on silicon substrates

The optical efficiency of GaN-based multiple quantum well (MQW) and light emitting diode (LED) structures grown on Si(111) substrates by metal-organic vapor phase epitaxy was measured and compared with equivalent structures on sapphire. The crystalline quality of the LED structures was comprehensively characterized using x-ray diffraction, atomic force microscopy, and plan-view transmission electron microscopy. A room temperature photoluminescence (PL) internal quantum efficiency (IQE) as high as 58% has been achieved in an InGaN/GaN MQW on Si, emitting at 460 nm. This is the highest reported PL-IQE of a c-plane GaN-based MQW on Si, and the radiative efficiency of this sample compares well with similar structures grown on sapphire. Processed LED devices on Si also show good electroluminescence (EL) performance, including a forward bias voltage of ∼3.5 V at 20 mA and a light output power of 1 mW at 45 mA from a 500×500 μm2 planar device without the use of any additional techniques to enhance the output cou...

Liquid injection metal organic chemical vapour deposition of nickel zinc ferrite thin films

Abstract Liquid injection metal organic chemical vapour deposition has been used to grow thin films of the single metal oxides of nickel, zinc and iron, the binary ferrites of nickel ferrite and zinc ferrite and the ternary nickel zinc ferrite. The precursor chemicals used for the deposition of the metal oxide layers were solutions of the metal thd compounds (thd=2,2,6,6-tetramethyl-3,5-heptanedionato) dissolved in tetrahydrofuran. The growth rates of the single metal oxide layers have been systematically determined as a function of substrate temperature in the temperature range 300–650°C and the ferrite layers were deposited at a substrate temperature of 500°C. The ferrite layers were polycrystalline with well-defined spinel crystal structures.

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.

Control of Growth Dynamics by Molecular Design in the MOCVD of Electronic Ceramics

The MOCVD technique is being used increasingly for the deposition of electronic ceramics such as Pb(Zr,Ti)O 3 , Ta 2 O 5 and TiO 2 . For the mil potential of MOCVD to be realised, it is sometimes necessary to modify existing precursors so that process parameters in the MOCVD process are optimised. In this paper we describe our approach to “molecular design” and discuss how the substitution of simple alkoxide groups by β-diketonates or donor-functionalised ligands can result in precursors with improved physical properties and optimum MOCVD characteristics.

Metalorganic chemical vapour deposition of manganese arsenide for thin film magnetic applications

Abstract Thin films of the ferromagnetic material manganese arsenide (MnAs) have been grown for the first time by atmospheric pressure metalorganic chemical vapour deposition (MOCVD), using tricarbonylmethylcyclopentadienyl manganese (TCM) and arsine. A detailed study of the MnAs growth characteristics are presented together with the resulting magnetic and structural properties.

CBE growth of GaAs/GaAlAs HBTs using the new DEAlH-NMe3 precursor and all-gaseous dopants

Abstract This paper describes the first reported use of diethylaluminium hydride-trimethylamine adduct (DEAlH-NMe 3 ) for the growth of GaAs/GaAlAs power heterojunction bipolar transistors (HBTs) by chemical beam epitaxy (CBE). This precursor possesses a significantly higher vapour pressure than the more conventionally used triethylaluminium (TEA), and leads to much less stringent requirements for bubbler and gas-line heating, and also much-improved GaAs/GaAlAs heterojunction definition when no carrier gas is employed. The use of all-gaseous n- and p-type dopants offers significant technological advantages in CBE, and the current paper also provides the first report of the use of hydrogen sulphide for n-type doping of CBE-grown GaAlAs HBT emitter regions. In conclusion, DC and RF data obtained from the heterojunction bipolar transistors fabricated to date are described. A DC gain of 40 has already been measured and encouraging early data obtained from RF-probed devices 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.