Metal-insulator-semiconductor Photodetector Research Articles

Photoresponse of the In 0.3 Ga 0.7 N metal–insulator–semiconductor photodetectors

In 0.3Ga 0.7N metal–insulator–semiconductor (MIS) and metal–semiconductor (MS) surface barrier photodetectors have been fabricated. The In0.3Ga0.7N epilayers were grown on sapphire by metalorganic chemical vapour deposition (MOCVD). The photoresponse and reverse current–voltage characteristics of the In0.3Ga0.7N MIS and MS photodetectors were measured. A best zero bias responsivity of 0.18 A/W at 450 nm is obtained for the In0.3Ga0.7N MIS photodetector with 10 nm Si3N4 insulator layer, which is more than ten times higher than the In0.3Ga0.7N MS pho-todetector. The reason is attributed to the decrease of the interface states and increase of surface barrier height by the inserted insulator. The influence of the thickness of the Si3N4 insulator layer on the photoresponsivity of the MIS photodetector is also discussed.

ZnO-based MIS photodetectors

We report the fabrication of ZnO-based metal–insulator–semiconductor (MIS) and metal–semiconductor–metal (MSM) photodetectors. With 5V applied bias, it was found that photocurrent to dark current contrast ratios of the ZnO MSM and MIS photodetectors were 2.9×102 and 3.2×104, respectively. It was also found that measured responsivities were 0.089 and 0.0083A/W for the ZnO MSM and MIS photodetectors, respectively, when the incident light wavelength was 370nm. Furthermore, it was found that ultraviolet (UV) to visible rejection ratios for the fabricated ZnO MSM and MIS photodetectors were 2.4×102 and 3.8×103, respectively.

Homoepitaxial ZnSe MIS photodetectors with SiO2 and BST insulator layers

ZnSe metal–insulator–semiconductor (MIS) photodetectors with SiO2 and Ba0.25Sr0.75TiO3 (BST) insulator layers were fabricated on ZnSe substrates. It was found that dark current densities of these MIS photodetectors were at least one order of magnitude smaller than ZnSe Schottky barrier photodetector without the insulator layers. UV-to-visible rejection ratios of these MIS photodetectors were also large, and the noise equivalent power (NEP) was 1.24×10−13 and 1.9×10−13 for the homoepitaxial ZnSe MIS photodetectors with SiO2 and BST insulator layers, respectively. The corresponding normalized detectivity (D∗) was 2.55×1012 and 1.67×1012cmHz0.5W−1, respectively. These values were better than those observed from the heteroepitaxial ZnSe photodetectors prepared on GaAs substrates.

Nitride-Based UV Metal–Insulator–Semiconductor Photodetector with Liquid-Phase-Deposition Oxide

A low-temperature (30–40°C), low-cost and reliable method of liquid phase deposition (LPD) has been employed to grow SiO2 layers on GaN. The LPD process uses a supersaturated acid aqueous solution of hydrofluosilicic (H2SiF6) as a source liquid and an aqueous solution of boric acid (H3BO3) as a deposition rate controller. In this study, the LPD SiO2 was prepared at 40°C with concentrations of H2SiF6 and H3BO3 at 0.2 and 0.01 M, respectively. The minimum interface-trap density, Dit, of a metal–insulator–semiconductor (MIS) capacitor with a structure of Al/20 nm LPD-SiO2/n-GaN was estimated to be 8.4×1011 cm-2 V-1. Furthermore, a MIS photodetector with a 10-nm-thick LPD-SiO2 layer has been fabricated successfully. The dark current density was as low as 4.41×10-6 A/cm2 for an applied field of 4 MV/cm. A maximum responsivity of 0.112 A/W was observed for incident ultraviolet light of 366 nm with an intensity of 4.15 mW/cm2. Defect-assisted tunneling was invoked to explain these results.

High UV/visible rejection contrast AlGaN/GaN MIS photodetectors

GaN-based metal-insulator-semiconductor (MIS) AlGaN/GaN ultraviolet (UV) photodetectors with photo-chemical vapor deposition (Photo-CVD) SiO 2 insulator and AR-coating layer were fabricated. It was found that with a 5 V applied bias, photocurrent to dark current contrast ratio was 1.27 × 10 4 for the MIS photodetector with AR-coating. It was also found that UV-to-visible rejection ratio of such MIS photodetector with AR-coating was more than 3 orders of magnitude while the responsivity was 0.144 A/W with a 5 V applied bias and a 350 nm incident light wavelength.