Optical absorption in sputtered amorphous phosphorus

Optical absorption measurements are reported on r.f. sputtered films of a-P prepared at variable substrate temperatures. With decreasing substrate temperature the absorption spectra shift to lower frequencies and the energy gap decreases. The form of the spectra are, however, similar both in the band edge and Urbach tail regions. The Urbach slope is found to differ substantially from that of a-As, indicating that factors other than coordination number may influence this parameter. The changes in the absorption spectra are suggestive of a possible role of intermediate range order on the electronic states in a-P.