THE ORIGIN OF METASTABLE STATES IN A-SI-H

Several reversible metastable phenomena are observed in the electronic properties of hydrogenated amorphous silicon (a-Si:H). Examples are the Staebler-Wronski effect, defects induced by electron accumulation at an interface and by space-charge-limited current flow, and thermally induced changes in the density of states. We present evidence that all these phenomena have a common origin. In each case the metastable effects are induced by changes in the Fermi energy position and are removed by bringing the electronic structure into thermal equilibrium at elevated temperatures. The structural changes that underlie the metastabilities are made possible by the diffusive motion of hydrogen.