K. Sugita

Single-crystalline InN films with an absorption edge between 0.7 and 2 eV grown using different techniques and evidence of the actual band gap energy

Single crystalline InN films with an absorption edge between 0.7 and 2 eV have been grown using a variety of different techniques, including conventional metal-organic vapor-phase epitaxy (MOVPE), ArF-laser assisted MOVPE (la-MOVPE), and plasma-assisted molecular-beam epitaxy (pa-MBE). Analysis of samples grown using different methods has led to important evidence for determining the actual band gap energy of InN. In an effort to find the origin of the change in absorption edge, this evaluation was focused on the la-MOVPE of InN. This deposition technique enables InN film deposition over a wide range of growth temperatures, ranging from room temperature to a very high temperature (700 °C). Characterization of InN films grown over a wide range of temperatures strongly suggests that oxygen contamination leads to a larger band gap absorption energy value than the actual value, even in the case of single crystalline films. In films grown at low temperatures, oxygen appeared to form an alloy, resulting in a la...

Barrier Thickness Dependence of Photovoltaic Characteristics of InGaN/GaN Multiple Quantum Well Solar Cells

We discuss the influence of the barrier thickness of an InGaN/GaN multiple quantum well (MQW) structure on solar cell performance. As barrier thickness decreases, short-circuit current density increases and open-circuit voltage decreases. The open-circuit voltage is much lower than expected from the absorption edge because of the large leakage current and large ideality factor of diodes owning to the carrier tunneling through the barrier. An MQW with a 3-nm-thick barrier layer shows a much longer carrier lifetime than that with a 9-nm-thick barrier layer. This is one possible reason for a higher short-circuit current in solar cell with the 3-nm-thick barrier MQW structure than that with the 9-nm-thick barrier MQW.

MOVPE-grown n-InxGa1-xN (x~0.5)/p-Si(111) template as a novel substrate

This paper proposes for the first time the preparation of n-InGaN/p-Si templates as substrates for InGaN device applications. By using MOVPE, a thick (~0.5 m) InGaN with an intermediate In composition has been successfully grown on Si(111) substrates using an AlN interlayer. By optimizing growth temperature and TMI/(TMI+TEG) molar ratio, InGaN films with In content up to 0.5 are successfully grown. Tensile stress in InGaN films grown at 700°C is estimated to be about half of that for GaN grown at 1100°C and no cracks are found in the InGaN layers. The films grown at a relatively high temperature (700-750°C) show phase separation when their thickness exceeds a critical value. Critical thickness for phase separation is larger for a film grown at a lower temperature with a high In content. For InGaN grown at 600°C with a thickness of 0.8 m, no phase separation is detected by both X-ray diffraction and PL. Such a low temperature-grown InGaN shows a large tilt fluctuation. Ohmic I-V characteristics are obtained between n-InGaN and p-Si and the resistance is markedly decreased with increasing In content in InGaN. The Si pn junction beneath the In0.42Ga0.58N layer behaves well as a solar cell with an InGaN filter. For both n-InGaN/p-Si, the presence of an AlN interlayer between the epilayer and the substrate does not have a significant contribution to the series resistance.

Catalyst Temperature Dependence of NH3 Decomposition for InN Grown by Metal Organic Vapor Phase Epitaxy

In this paper, we report an independent catalyst heating system on the Pt-catalyst metal organic vapor phase epitaxy (MOVPE) for Indium nitride (InN) growth, and the dependence of the NH3 decomposition rate on the Pt catalyst temperature (RT to 1000 °C) using a quadrupole mass spectrometer (Q-MS). When the catalyst temperature is increased above the growth temperature of InN, the NH3 decomposition rate is enhanced. The grain size of InN becomes larger and the full width at half maximum (FWHM) of the X-ray rocking curve (XRC) was drastically decreased. The increase of N atoms results in the incorporation of nitrogen into the InN layer and thus improves the crystal quality of InN. However, active H increases sharply when the catalyst heater temperature is over about 850 °C. Therefore, a great improvement in the crystal quality of InN film is expected by optimizing the growth condition including a catalyst temperature not exceeding 850 °C.

High-resolution X-ray diffraction analysis of InN films grown by metalorganic vapor phase epitaxy

The growth temperature dependence of the InN films crystalline quality is reported. InN films are grown on sapphire substrates from 570 to 650 degrees C with low-temperature GaN buffers by metalorganic vapor phase epitaxy (MOVPE). The X-ray rocking curves and reciprocal space mappings of the symmetric reflection (0 0 0 2) and asymmetric reflection (1 0 (1) over bar 2) are measured with high resolution X-ray diffraction. The results indicate that the crystallinity is sensitive to the growth temperature for MOVPE InN. At growth temperature 580 degrees C, highly crystalline InN film has been obtained, for which the full-width-at-half-maxima of (0 0 0 2) and (1 0 (1) over bar 2) rocking curves are 24 and 28 arcmin, respectively. The crystalline quality deteriorates drastically when the growth temperature exceeds 600 degrees C. Combined with the carrier concentration and mobility, the approach to improve the quality of InN film by MOVPE is discussed