Photocurrent multiplication in Ga2O3/CuInGaSe2 heterojunction photosensors

Photocurrent multiplication was observed in gallium oxide (Ga2O3)/Cu(In,Ga)Se-2 (CIGS) heterojunction photosensors. In this study, we investigated the electrical and optical properties of Ga2O3/CIGS heterojunction photodiodes for possible use as high-sensitivity visible-light sensors. To achieve low current density J under dark conditions, a thin layer of Ga2O3, which is an n-type wide band gap (4.7-4.9 eV) semiconductor, was grown on the CIGS layer. This Ga2O3 layer functioned as a hole-blocking layer and buffer layer. The effect of oxygen partial pressure during the deposition of the Ga2O3 layer was also examined. With no applied voltage, the quantum efficiency of a photodiode with a Ga2O3 layer deposited with no oxygen partial pressure was considerably high. On the other hand, when the Ga2O3 layer was deposited with oxygen partial pressure, the depletion region almost spread into the Ga2O3 layer with no applied voltage. Considering J, under low oxygen deposition conditions, dark current J increased due to more oxygen vacancies, and with higher oxygen partial pressure during deposition, dark current J increased due to oxygen plasma damage at the Ga2O3/CIGS interface during the sputtering deposition. The photodiode with the lowest dark current J of 10(-9) A/cm(2) at applied voltages less than 3 V had a Ga2O3 layer deposited at an optimum oxygen partial pressure of 6.0 x 10(-2) Pa. The average quantum efficiency for this photodiode in the visible light range (400-700 nm) was 85% at an applied voltage of 3 V. Moreover, at higher applied voltages, carrier multiplication phenomena were observed, and the average quantum efficiency (400-700 nm) was over 100% at applied voltages over 4V. (C) 2015 Elsevier B.V. All rights reserved.