We use total-yield photoelectron spectroscopy in combination with the Kelvin probe to obtain a simple and direct determination of the distribution of occupied states over nearly the entire band gap in P-doped $a-\mathrm{S}\mathrm{i}:\mathrm{H}$. The large dynamic range (${10}^7$:1) and high energy resolution $\Delta E\le 0.1$ eV) of this electron-emission spectroscopy also allow the distribution of unoccupied states above the Fermi level to be determined by division of the measured spectra by the Fermi occupation function. We exploit this novel capability to prove that the conduction-band tail in P-doped $a-\mathrm{S}\mathrm{i}:\mathrm{H}$ is exactly exponential.

• Received 22 February 1988

DOI:https://doi.org/10.1103/PhysRevLett.60.2697