Blue-Violet Avalanche-Photodiode (APD) and its Ionization Coefficients in II-VI Wide Bandgap Compound Grown by Molecular Beam Epitaxy

Abstract

We present II-VI wide bandgap semiconductor ZnSe and ZnSSe based blue-violet avalanche photo-diode (APD) operation grown on GaAs substrate by molecular beam epitaxy (MBE). Because of highly improved crystal quality of the active layer, the ZnSSe APD reveals stable and high avalanche gain (G ! 60) in the blue-violet optical region under high field operation condition (E ¼ 1.15 Â 10 6 V/cm) at room temperature (RT). High electric field induced ionization coefficients a (for electrons) and b (for holes) are determined as a function of electric field strength E(V/cm); a(E) ¼ 1.7 Â 10 7 exp (--4.9 Â 10 6 /E) and b(E) ¼ 3.7 Â 10 6 exp (--4.0 Â 10 6 /E).Introduction Recently, very active research and development on the blue-ultraviolet photodetectors using II-VI and III-V wide bandgap semiconductors have been made for new applications of a large capacitive optical storage system, medical instruments, and flame sensing, etc. So far, a large potential of ZnSe-based detectors have been reported by many authors where the p-n and p-i-n junction photodiodes reveal high external quantum efficiencies exceeding 80% (in the blue region) [1][2][3][4][5][6].For applying these photodiodes to practical applications, stable high field operation is required. In this paper, we present a stable high field operation of a new ternary ZnSSe APD device. We performed growth of high quality ZnS x Se 1--x (x ¼ 5-6%) films by precise control of the complete lattice matching to GaAs substrate. The improved ZnSSe APD reveals large avalanche gain (G ! 60) under electric field strength of 1.15 Â 10 6 V/cm.We also present important device parameters, high field induced ionization coefficients of photo-injected carriers (electrons and holes), which are important parameters for the optimum design of the wide bandgap compound-based APD devices.