MIS Tunnel Diodes: Application to Solar Energy Conversion

Abstract

<p> The MIS tunnel solar cell has recently attracted most of the attention in the solar energy conversion field. Construction is very simple and eliminates the costly diffusion of dopants. As in the Schottky type, a metal of proper work function is chosen to induce an inversion layer at the surface of the semiconductor (Al in the case of p type Si). An ultra thin (< 1.5 nm) oxide between the semiconductor and the metal passivates the surface by reducing surface states while permitting tunneling from the semiconductor to the metal.</p> <p> Good fill factors (> .7) have been obtained but high reflectivity of the Al has reduced the current output. Open circuit voltages greater than .61 volts and short circuit current density of 21 ma/cm^2 have been measured. Experimental evidence of the presence of an oxide different from SiO2 within 1.4 nm of the surface will be given and related to the thickness variation of the open circuit voltage. A maximum in VOC around 1.4 nm was found. A maximum efficiency of 7% was achieved without anti reflexion coating and a curve factor of .81 was observed in one of the cells. A slight variation in efficiency with the cell area was also observed.</p>