Hydrogen Incorporation in Crystalline Semiconductors

Abstract

Hydrogen is, in principle, the simplest impurity in semiconductor materials. It is a common constituent of many chemicals and gases used in the growth and processing of semiconductor crystals, and with its high diffusivity even near room temperature, hydrogen is readily incorporated into these materials. This incorporation is not always intended or even realized. The presence of hydrogen can be detected by direct means, such as mass spectrometry or ion-beam analysis, but in general its presence is betrayed by the changes it causes in the electrical and optical properties of the semiconductor. These changes are beneficial in disordered materials such as the amorphous [2.1] or polycrystalline [2.2] Si used to make solar cells. The addition of hydrogen in these cases acts to reduce the density of electrically active dangling bonds and dislocations, respectively, and the advances in solar-cell technology over the past two decades are due, in no small part, to the use of hydrogen passivation techniques [2.3]. The net effect of hydrogen incorporation in disordered semiconductors is to make them more like their ordered counterparts. That is, the luminescent efficiency of amorphous or polycrystalline Si improves upon hydrogenation, while there is a decrease in parameters such as reverse bias leakage currents in diode structures. These currents are usually dominated by defect-related processes such as generation-recombination and tunnelling.