Characterization of interface states in thin epitaxial film In0.75Ga0.25P/Ag diodes

Abstract

Epitaxial In0.75Ga0.25P/Ag Schottky contacts were fabricated by electron beam evaporation of Ag on an epitaxial thin film of In0.75Ga0.25P grown on highly doped n‐InP substrate by MOCVD. The diode showed non‐ideal behavior with an ideality factor of 1.3 and is thought to have a metal‐interface layer‐semiconductor (MIS) structure. The room temperature small signal ac capacitance (Cm) was measured as a function of applied voltage (Va), in the frequency (f ) range 0.5 KHz and 1 MHz. Under forward bias, the large frequency dispersion in Cm was attributed to the interface states in equilibrium with the semiconductor (In0.75Ga0.25P). From Cm, the interface states capacitance Cp was extracted. The experimental Cp−f data fitted well to Lehovec’s model of an interface state continuum with a single time constant and provided the values of the interface states energy density (Nss), relaxation time (τ) and capture cross‐section (σn) for forward bias (Va) voltages between 0.0 V and 0.4 V. Over the forward bias range 0.4V>Va>0.0V,Nss decreased linearly with bias from 1.7×1012 eV−1cm−2 to 2.4×1011 eV−1cm−2 and σn increased exponentially with bias from 1.9×10−15 cm2 to 3.9×10−9 cm2.