Density of states in tritiated amorphous silicon obtained with the constant photocurrent method J. Appl. Phys. 98, 093705 (2005); 10.1063/1.2123374Density of states in the gap of amorphous semiconductors determined from modulated photocurrent measurements in the recombination regime Electron time-of-flight transient photocurrents have been investigated in stabilized a-Se as a function of electric field, annealing, aging ͑relaxation͒, and alloying with As and doping with Cl. The distribution of localized states ͑DOS͒ in stabilized a-Se has been investigated by comparing the measured and calculated transient photocurrents. The samples were prepared by conventional vacuum deposition techniques. The theoretical analysis of multiple-trapping transport has been done by the discretization of a continuous DOS and the use of Laplace transform formalism. The resulting DOS has distinct features: A first peak at ϳ0.30 eV below E c with an amplitude ϳ10 17 eV −1 cm −3 , a second small peak ͑or shoulder͒ at 0.45-0.50 eV below E c with an amplitude 10 14 -10 15 eV −1 cm −3 , and deep states with an integral concentration 10 11 -10 14 cm −3 lying below 0.65 eV, whose exact distribution could not be resolved over the time scale of present experiments. The influence of doping, aging, annealing, and substrate temperature on the DOS distribution has been investigated. The doping with Cl does not affect the amplitudes of the first and second peaks while the concentration of deep states increases dramatically. The alloying with As reduces the density of deep states and seems to increase the amplitude of first and second peaks. The aging substantially reduces the deep states density and the amplitude of the second peak while the amplitude of the first one remains practically unchanged. The results have been interpreted primarily in terms of thermodynamic and intrinsic structural defects in the chalcogenide glass structure.