Photoinduced Absorption in Amorphous Tetrahedrally  Semiconductors.
Abstract
A photoinduced transient absorption (PA) was observed and studied in amorphous semiconductors and alloys prepared by methods which incorporate hydrogen. In aSi:H the induced adsorption coefficient has the form (DELTA)(alpha)(H/2PI)(omega) = c((H/2PI)(omega)  E(,t))(' 1/2) in the spectral range 0.25  1.5 eV. The threshold energy E(,t) is (0.45 (+OR ) 0.09) eV and c (TURNEQ) 21 eV(' 1/2) cm('1) at 80 K for excitation by (TURN) 1 W/cm('2) of argon laser light. The absorption arises from transitions between holes trapped at deep lying defects and the valence band. In aGe:H the PA spectrum consists of an isolated symmetric band and we interpret the absorption mechanism as photonassisted hopping of small polarons bound to defects with a binding energy of 0.35  0.40 eV. Recombination of these excitations is found to follow bimolecular diffusion limited kinetics. The electron drift mobility can be determined from the recombination rate and is a decreasing function of time following pulsed excitation ((mu) (TURN) t('.3)). The time averaged mobility in undoped aSi:H is (2.4 (+OR) 1.7) x 10('3) cm('2)/V sec at room temperature and decreases with decreasing temperature as exp (T/T(,1)) with T(,1) = 31 K, 67 K, and 106 K in undoped, B and P doped aSi:H respectively. The unusual time and temperaturedependences of (mu) are evidence of the important influence of localized states on the transport properties of amorphous semiconductors.
 Publication:

Ph.D. Thesis
 Pub Date:
 1980
 Bibcode:
 1980PhDT........36O
 Keywords:

 Physics: Condensed Matter