Search

Nitridation process of a sapphire surface was investigated with atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), and X-ray photoelectron spectroscopy (XPS) in order to reveal a general nitridation mechanism. It was found that the nitridation process consists of two steps. First, inter-mixing between nitrogen-related species and sapphire surface occurs forming hydrogenated Al oxynitride. This step does not change the surface morphology significantly. Second, crystalline AlN islands are gradually formed by further nitridation of hydrogenated Al oxynitride, resulting in a very rough surface.

Metalorganic molecular-beam epitaxy of InGaP, InAlP, and AlGaP was investigated at various temperatures (290–650°C), using triethylindium (TEIn), triethylgallium (TEGa), triethylaluminum (TEAl), and phosphine. Three distinct stages were observed in the temperature dependence of growth rate and epilayer composition of those ternaries. At lower temperatures below 390°C the incomplete pyrolysis of TEGa and TEAl limits the growth, while TEIn decomposes perfectly as low as 290°C. TEAl decomposition is incomplete at all the temperatures studied, and is enhanced by the existence of TEIn or TEGa. To explain this observation, a co-decomposition mechanism was proposed, in which thermal energy produced by the pyrolysis of TEIn or TEGa induces the decomposition of TEAl; complexes such as TEAl-TEIn and TEAl-TEGa are assumed to be formed by mixing the metalorganics in the vapor phase. In the moderate-temperature region of 390–520°C, the growth is limited by the supply of metalorganics. At higher temperatures above 520°C phosphorus evaporates from the superficial part of epilayers with breaking bonds of In-P, resulting in many indium droplets on the epilayer surfaces. The incorporation of gallium and aluminum atoms into the indium droplets reduces the growth rate of the GaP and AlP constituents in InGaP and InAlP epitaxy. By the absence of In-P bonds, the growth rate of AlGaP does not decrease up to 650°C, and no droplets are formed on the surfaces.

Crystal growth of InGaP and InAlP was carried out on GaAs(100) by MOMBE using TEIn, TEGa, TEAl and PH 3 . Three distinct stages were observed in the temperature dependence of the growth rate and the Ga composition x of In 1− x Ga x P epilayers. The growth rate and the Ga composition increased with temperature up to 420°C, while they were constant at 420–520°C. By dividing the growth rate γ of In 1− x Ga x P into the two growth rates of quasi-binaries ( x γ for GaP and (1− x )γ for InP), the pyrolysis of TEGa was found to limit the growth below 420°C. Beyond 520°C, the growth rate decreased rapidly while the Ga composition increased. The formation of metal droplets on the epilayer surface above 520°C suggests that phosphorus evaporation governs the growth at higher temperatures. A quite similar temperature dependence was observed in In 1− x Al x P growth. The small activation energy in TEA1 decomposition is discussed.

A new type of immiscible growth of In1−xGaxP on GaAs was observed in low-vacuum (0.03 Torr) MOVPE. From the compositional separation observed as two separated peaks of (200) in an X-ray diffraction pattern, the surface morphology of the immiscible In1−xGaxP layer, and an analysis for the distribution of In and Ga by EPMA, it was found that InP-rich crystallites were formed in a GaP-rich flat layer. To explain the immiscible growth of In1−xGaxP in low-vacuum MOVPE, a growth model was constructed based on a modification of a thermodynamic explanation of immiscibility. By this model, three types of the crystal growth (immiscible In1−xGaxP, normal In1−xGaxP and InP growth on GaAs) were explained, consistently with surface morpologies.

InP and InGaP crystal growth on GaAs(100) was carried out by low-vacuum (0.03 Torr) MOVPE. Single crystals of InGaP were obtained on GaAs when the substrate temperature was 670°C. In this low-vacuum MOVPE growth of InGaP, as in conventional MOVPE, the growth rate is limited by the supply of group-III metalorganics, and Ga-element is taken into the grown layer more effectively than In-element. In some cases, immiscible InGaP growth was observed as a compositional separation in the grown layers when the substrate temperature was below 620°C. A model for the crystal growth in low-vacuum MOVPE, which can explain the occurence of the immiscibility, is proposed.