Naohiro Kuze

InAs deep quantum well structures and their application to Hall elements

Abstract We have investigated new InAs deep quantum well structures (InAs DQWs) made from InAs/AlGaAsSb materials on GaAs substrates by molecular beam epitaxy (MBE). In the InAs DQWs, AlGaAsSb layers are lattice matched to InAs. High electron mobilities of more than 20000 cm 2 / V · s at room temperature have been obtained in a wide range of substrate temperature and Al composition of Al x Ga 1− x AsSb layers (0 ≤ x ≤ 0.8). The InAs DQWs have been applied to Hall elements (HEs) for the first time. The new type of HEs with InAs DQWs (InAs DQWHEs) show superior characteristics, such as output voltage as high as 520 mV (at V in = 6 V , B = 0.1 T ), small dependence of input resistance on temperature and good reliability for practical use.

Surface Acoustic Wave Properties of Lithium Tantalate Films Grown by Pulsed Laser Deposition

Single-crystal films of lithium tantalate ( LiTaO3) have been grown on sapphire substrates (001), (110) and (012) by pulsed laser deposition. Surface acoustic wave (SAW) and optical properties of these films have been investigated. The refractive indices of a (012) LiTaO3 film are n e=2.1712 and n0=2.1651 at 632.8 nm. The SAW velocities of propagation (V s), the temperature coefficients of the center frequency (TCF) and the electro-mechanical coupling coefficients (k2) of the films have been measured, and theoretical calculations of V s and k2 have been done. Experimental V s and k2 coincide with calculated ones. Theoretical calculations show that LiTaO3 films deposited by pulsed laser deposition are superior materials for high frequency SAW devices.

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.

High-Sensitivity Temperature Measurement With Miniaturized InSb Mid-IR Sensor

This paper reports the development and evaluation of an InSb photovoltaic infrared sensor (InSb PVS) operating at room temperature. The InSb PVS consists of 700 InSb p⁺ - p^- - n⁺ photodiodes connected in series, on a semi-insulating GaAs (100) substrate. An Al_0.17rIn_0.83Sb barrier layer between p⁺ and p^- layers was used to reduce diffusion of photo-excited electrons. Cutoff wavelength was 6.8 mum and output signal was almost linear with irradiance up to 0.6 mW/cm². Sensitivity of 67 muV/K and noise equivalent temperature difference of 2.2 mK/Hz^1/2 was obtained at room temperature, which shows the sensor to be a suitable for noncontact thermometry.

Molecular beam epitaxial growth of high electron mobility InAsAlGaAsSb deep quantum well structures

We investigated InAs deep quantum well structures made from InAs/AlGaAsSb materials on GaAs substrates by molecular beam epitaxy. By accurately controlling As 4 /Sb 4 and As 4 /In beam flux ratios, we were able to grow the high-quality crystals of AlGaAsSb and InAs. Very high electron mobility of more than 32,000 cm 2 /Vs were obtained at room temperature. It was found that the optimum beam-equivalent-pressure (BEP) ratio of As 4 /In for growing an InAs quantum well layer is 110 to get the highest electron mobility. Moreover, a strong photoluminescence (PL) peak of AlGaAsSb band-edge emission at 10 K was observed around 1.2 eV. We determined that the optimum As 4 /Sb 4 BEP ratio is 6.7 for AlGaAsSb from the full width at half-maximum of PL peaks and electrical characteristics. We also observed the blue shifted PL of AlGaAsSb as the As 4 /Sb 4 BEP ratio decreased.

InSb Mid-Infrared Photon Detector for Room-Temperature Operation

We developed a small InSb mid-infrared (2–7 µm wavelength range) photon detector that operates at room temperature. The photodiode was made from (hetero epitaxial) InSb layers that were grown on a semi-insulating GaAs substrate by molecular beam epitaxy. To suppress the effects of the diffusion current of the p–i–n photodiode, we used an AlInSb barrier layer that raises the resistance of the photodiode. We also optimized the devices doping concentration and the infrared incidence window structure. These optimization steps realized high photoelectric current output in a room-temperature environment. We also increased the signal-to-noise ratio of the detector by connecting multiple photodiodes in series. The size of this detector is 1.9×2.7×0.4 mm3 and the detectivity is 2.8×108 cm Hz1/2/W at 300 K. This is a practical IR detector that can be used in general signal amplification ICs.

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.

MBE research and production of Hall sensors

Abstract The market for magnetic sensors has been growing rapidly. In 1995, Asahi Kasei Electronics (AKE) commercially produced over 800 million InSb high-sensitivity Hall sensors (which amounts to 70%, of the world market) by vacuum deposition. InAs Hall sensors having good noise properties and small temperature dependence have also been developed by mass production molecular beam epitaxy (MBE). Further, InAs deep quantum well (InAs DQW) Hall sensors with high sensitivity and good stability under a wide temperature range are opening up new applications of magnetic sensors. Hall sensors have now become an important application for III-V compound semiconductors.

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

Reflection high-energy electron diffraction image analysis during molecular beam epitaxial growth of InAs/AlGaAsSb deep quantum well structures

We have investigated the lattice strain relaxation during the initial stage of Alx Ga1-x AsSb (0<x<0.5) growth on GaAs (100) substrates by molecular beam epitaxy (MBE). Using time-resolved reflection high-energy electron diffraction (RHEED) image analysis, we have found that AlGaAsSb on a GaAs surface quickly relaxes within 3 to 7 monolayers (MLs). We have also observed that two-dimensional (2D) growth occurs after deposition of 20MLs of GaAsSb on GaAs surfaces. Furthermore, we have confirmed the InAs grows on AlGaAsSb two-dimensionally because AlGaAsSb is lattice matched to InAs. With a total thickness of less of than 700 nm in the InAs/AlGaAsSb deep quantum wells (DQWs), we have achieved very high electron mobilities of more than 32,000 cm2/(Vs) at room temperature.