Novel Structure for Measuring the Density-of-State Distribution of High-Resistivity Semiconductor Films by Isothermal Capacitance Transient Spectroscopy

A novel structure, metal/high-resistivity semiconductor (HRS)/n-type c-Si substrate with the space charge region (SCR) entirely covering the HRS film and penetrating into the c-Si substrate, has been proposed for determining the density-of-state distribution g(E) of the HRS films via the isothermal capacitance transient spectroscopy (ICTS) method. The structure has been tested and applied to the measurement of g(E) of the undoped hydrogenated amorphous silicon (a-Si:H) film. For undoped a-Si:H film with optical gap E _o=1.72 eV, a peak in g(E) is observed at 0.66 eV below the conduction band mobility edge E _c, with the attempt-to-escape frequency of v_n=1.61× 10¹³ s^-1. These midgap states are surmised to be correlated with the doubly occupied dangling bond D^-.