Yutaka Hamamura

Characterization of GaN Based UV-VUV Detectors in the Range 3.4–25 eV by Using Synchrotron Radiation

The characterization of Schottky type ultraviolet (UV) detectors with transparent electrode between vacuum ultraviolet (VUV) and visible light region using synchrotron radiation is described. The responsivity spectrum of the detectors at 0 V bias was obtained in the wide range between 2 eV (563 nm) and 25 eV (50 nm). The photoemission current from Au electrode was able to be canceled by improving the measuring circuit, and thus we succeeded in operating the detectors without any photoemission current from Au and GaN. The responsivity of the detectors is about 0.15 A/W at 3.5 eV. These results show that these Schottky type detectors with the transparent electrode are effective to detect VUV-UV light (50-360 nm, 3.4-25 eV) without any photoemission.

Characterization of GaN-Based Schottky Barrier Ultraviolet (UV) Detectors in the UV and Vacuum Ultraviolet (VUV) Region Using Synchrotron Radiation

Characterization of GaN-based Schottky barrier ultraviolet (UV) detectors with a comb-shaped electrode using synchrotron radiation (hν=2.2–30 eV, λ=41–563 nm) is described. Below hν=8.0 eV (λ>155 nm), the detectors are available without any photoemission of GaN and Au electrode. Under application of reverse bias, the responsivity is increased to 0.05 A/W at -0.4 V. The photocurrent is controlled by reverse bias. On the other hand, above hν=8.0 eV (λ<155 nm), the responsivity spectra are dominated by photoemissions of Au and GaN. These results show that these Schottky type detectors with mesa structures are effective to detect vacuum ultraviolet (VUV)-UV light (155

Growth of CuGaS2 single crystals by the traveling heater method using CuI solvent

Abstract Growth of CuGaS 2 single crystals by the traveling heater method (THM) using CuI solvent has been investigated. Bulk CuGaS 2 single crystals were obtained by the THM growth using CuI zone solutions containing Cu-excess and/or Ga-excess non-stoichiometric solutes. The color of the obtained crystals was greenish yellow or yellow, corresponding to the solute compositions. Electrical and optical characteristics have been studied for the crystals.

Fabrication and characterization of UV Schottky detectors by using a freestanding GaN substrate

GaN ultraviolet (UV) detectors were fabricated on a freestanding GaN substrate with low dislocation density. The resulting dark current density was below 1 nA/cm-2 at -8 V reverse bias, which was about 3 orders of magnitude lower than that of a similar detector made on a sapphire substrate. Moreover, the ideality factor was nearer to unity than the device on a sapphire substrate. In addition, by comparing the GaN-based device to a commonly used Si photodetector, we found that the GaN device had a lower signal-to-noise ratio and greater temperature stability. Therefore, we found a drastic reduction of dark current by using GaN freestanding substrates and so the GaN substrate produced a more effective detector than the sapphire substrate.