AbstractWe analyze the transient response of i/n/i and i/p/i semiconductor structures in terms of space-charge-limited and emission-limited currents. In this ‘sweep-out’ experiment, an initial space-charge-limited current governed by the i-layer characteristics gives way at later times to an emission-limited current from the doped layer. The emission-limited current response can be used as a new spectroscopy for determining the electronic density of states near the mobility edge of doped semiconductors. We summarize the published experimental sweep-out data and draw conclusions about the density of electronic states of both n-type and p-type hydrogenated amorphous silicon.