Enhanced photogeneration of carriers in a semiconductor via coupling across a nonisothermal nanoscale vacuum gap

Enhanced generation of carriers when a thermophotovoltaic cell is placed in submicron proximity to a heated surface is demonstrated using custom-desig ned InAs photodiodes and special silicon-based heater chips produced using microelectromechanical system techniques. The short-circuit current of the photocells is shown to increase sharply (up to fivefold) when the spacing b etween the heater and photodiode surfaces is reduced, while at the same tim e, the heater temperature decreases, consistent with increased radiative tr ansfer between the two surfaces. By varying the spacing sinusoidally (at up to 1 kHz), it is demonstrated that the increase in the short-circuit curre nt occurs in phase with the decrease in separation, thereby ruling out ther mal effects. It is argued that the increase in short-circuit current is due to increased evanescent coupling of blackbody radiation from the hot surfa ce to the cold photocell, consistent with recent theoretical predictions. T he demonstration of this effect is the initial step in the development of a class of energy conversion devices. (C) 2001 American Institute of Physics .