Yoshitaka Moriyasu

In situ monitoring of reflection high-energy electron diffraction oscillation during the growth of gallium nitride films by gas-source molecular beam epitaxy

Abstract Reflection high-energy electron diffraction (RHEED) specular intensity oscillations have been observed during the growth of gallium nitride (GaN) films by gas-source molecular beam epitaxy (GS-MBE) for the first time. The GaN films were grown on sapphire substrates using metal gallium and ammonia as source materials, following the deposition of a GaN buffer layer at lower temperature. The incident electron beam was parallel to the GaN [1 1 00] azimuth direction and the signal intensity was measured with a photo-multiplier via an optical fiber fixed on the specular spot. The total thickness of the film was 1700 A which includes the 180 A buffer layer. RHEED oscillations during growth were observed on the sapphire (0001) substrate. Comparing the period of the RHEED intensity oscillations with those calculated from the growth rate, we found that a single period of the RHEED intensity oscillation corresponds to a monolayer growth of GaN.

Miniaturized InSb photovoltaic infrared sensor operating at room temperature

This paper reports the development of a novel InSb photovoltaic infrared sensor (InSb PVS) operating at room temperature. The InSb PVS consists of an InSb p+/p-/n+ structure grown on semi-insulating GaAs (100) substrate, with a p+ Al0.17In0.83Sb barrier layer between p+ and p- layers to reduce diffusion of photo-excited electrons. Photodiodes were fabricated by wet etching process and, using a 500K blackbody, we obtained D* of 2.8x108 cmHz1/2/W and RV of 1.9 kV/W at room temperature. S/N was improved with the serial connection of 700 photodiodes patterned on a 600x600 μm2 chip. Increasing the number (N) of connected photodiodes, S/N ratio was improved by a factor of N1/2. RV was constant for signals ranging from DC to 500Hz. From spectral response measurements a cut-off wavelength of 6.8 μm was obtained. The InSb PVS was flip-chip bonded on a pre-amplifier IC, allowing the shortest connection between the InSb PVS and the pre-amplifier, making the system immune to electromagnetic noise. The system was finally encapsulated by a Dual Flat Non-leaded (DFN) package with a window, which exposes the backside of the GaAs substrate allowing the infrared light incidence. The device external sizes are 2.2 mm x 2.7 mm x 0.7 mm and to our knowledge is the smallest uncooled sensor for the middle-infrared range reported until now.

A Novel InSb Photodiode Infrared Sensor Operating at Room Temperature

A microchip-sized InSb photodiode based infrared sensor (InSb PDS) that operates at room temperature was developed. The InSb PDS consists of 700 photodiodes connected in series and consumes no power, because it works in photovoltaic mode to output an open-circuit voltage. The InSb PDS has a typical responsivity of 1,900 V/W and an output noise of 0.15 μV/Hz 1/2 . A detectivity of 2.8×10 8 cmHz 1/2 /W was obtained at 300 K. The InSb PDS has performance high enough for applications such as mobile electronic equipment, personal computers, and consumer electronics

Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by x-ray diffraction

The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.