Photoassisted tunneling from free-standing GaAs thin films into metallic surfaces

Abstract

Abstract.The tunnel photocurrent between a gold surface and a free-standing semiconducting thin film excited from the rear by above bandgap light has been measured as a function of applied bias, tunnel distance and excitation light power. The results are compared with the predictions of a model which includes the bias dependence of the tunnel barrier height and the bias-induced decrease of surface recombination velocity. It is found that i) the tunnel photocurrent from the conduction band dominates that from surface states. ii) At large tunnel distance the exponential bias dependence of the current is explained by that of the tunnel barrier height, while at small distance the change of surface recombination velocity is dominant.

Electrowetting at a liquid metal-semiconductor junction

“…The difference between the low frequency and high frequency C-V curves can be used to estimate 4 the surface state density D s which we consider in a first approximation to be constant, although this is known not to be the case. 36 The C-V measurement yield values of D s corresponding to 2.98 Â 10 11 states m À2 eV À1 and 3.48 Â 10 11 states m À2 eV À1 for the n-type and the p-type silicon surfaces used here. These measured values for the silicon surface state density D s agree well with measured values for silicon surfaces 35 and also using Hg-Si system.…”

Photoassisted Fowler-Nordheim-like tunneling from passivated GaAs microcantilevers

“…Assuming a normal tunneling process without image charge effects (d 2 ≈ d) one finds that, to first order in 15 Here, (qV ph ) −1 = −d/(2d 0 * b ), implying that the slope of the exponential dependence of the photocurrent on tunnel bias should decrease with distance. 15 Although this prediction is qualitatively in agreement with curves a, b, and c of Fig. 2, quantitative analysis shows that FN-like tunneling (d 2 < d) cannot be neglected.…”

“…2, obtained by adding the quantity V * ∂I dark /∂V , where V * is given in Table I reveals, as found elsewhere, a power-law dependence with exponent f = 0.8. 15 In order to interpret the inflexion point, I dark is considered equal to the Schottky current I s , imply, as assumed by the above qualitative picture, an increase of δφ bd = φ d − qV sd due to an increase qV sd that leads to a decrease of both I dark and I s . The light-induced photovoltage alone can only induce a decrease of δφ bd and cannot interpret the results.…”

“…The photoelectron concentration n s per unit area at the tunneling energy E depends on bias because of a possible bias dependence of the surface recombination velocity. 15 The probability D(E) of the tunnel process is given by…”

“…The native oxide covering the GaAs cantilever is replaced by a monolayer of nitrogen using a recently developed hydrazine-sulfide treatment followed by annealing in an inert gas atmosphere at 500 • C. 13,14 The experimental setup and procedure have been described before. 15 After stabilization of the dark current (I dark ) to a set current at a bias of V c = −1.5 V, the feedback loop is opened and two bias scans are performed, one with the laser on and the second one in the dark. The difference between the measured currents is the tunneling photocurrent (I ph ).…”