A generalized approach to surface photovoltage

Abstract

A detailed majority and minority carrier current balance model for surface photovoltage (SPV) is presented. A rigorous treatment of carrier junction generation and surface recombination is shown to be essential. We show that under weak above band gap photoexcitation, standard constant open-circuit voltage and constant photon flux SPV measurements can both reveal the bulk minority carrier diffusion length, provided the initial band bending Vbi is sufficiently high. However, when Vbi is small, approximate SPV expressions are inapplicable and both standard SPV manifestations will then yield incorrect diffusion length values. We also show that for cases of low surface recombination velocity, the SPV technique can be used to measure the width of the space charge region and Vbi; however, when the surface recombination velocity is large, this approach cannot be used as majority carrier backdiffusion can play a dominant role under high photon energy excitation conditions.

Surface photovoltage phenomena: theory, experiment, and applications

“…It was usually found to be satisfactory (i.e., introducing an error of several percent at most) for free surfaces as well as Schottky contacts, including cases with minority carrier trapping. The one clear exception is cases where the SPV is a signi®cant portion of V 0 s [535] or that V 0 s is very small to begin with [89]. In these cases, SCR-related current components may be of the same order of magnitude as the minority carrier diffusion current, resulting in very signi®cant errors in the determination of L.…”

“…The latter is merely an approximation, which assumes that all SCR generation/recombination processes may be effectively lumped in a single SRV-like parameter. This assumption has been examined by increasingly elaborate numerical simulations as well as analytical developments [77,78,80,89,441,532,535,536]. It was usually found to be satisfactory (i.e., introducing an error of several percent at most) for free surfaces as well as Schottky contacts, including cases with minority carrier trapping.…”

“…Darling [33] performed a complete current balance, but assumed a constant recombination rate throughout the SCR ± an assumption which is not always realistic. The recent analysis of Liu et al [89] is the most advanced one in the sense that it makes a full current analysis with realistic SRH statistics. However, it is limited to the case of a negligible change in Q ss .…”

“…Due to the inadequacy of the FQL approximation for some free surface SPV problems, a similar theoretical approach was adapted in the 1990s by some authors not only for metal±semiconductor studies but also for free surface studies [33,88,89]. Konstantinov and Tsarenkov [88] assumed that generation and diffusion currents dominate the minority carrier behavior and thermionic emission dominates the majority carrier behavior.…”

Electroreflectance and surface photovoltage spectroscopies of semiconductor structures using an indium–tin–oxide-coated glass electrode in soft contact mode

“…In surface photovoltage, [22][23][24][25][26][27][28][29] we measure the change in surface potential due to optically excited electronhole pair generation under periodic illumination and subse- quent carrier redistribution and/or capture in the surface states. Recently, SPV has emerged as a powerful technique 5 to study surface states, [30][31][32][33][34][35] heterojunctions, 36,37 quantum wells, [38][39][40] and other nanostructures. [41][42][43] Various techniques like the Kelvin probe method, [44][45][46] MIS structure, 47-51 directcontact measurements like the electrolyte method, 52 depositing a semitransparent metallic contact, [53][54][55][56][57] or depositing a transparent conductor 58-60 on the sample have been used to measure the SPV.…”