An evaluation of phase-shift analysis of modulated photocurrents

The role of the recombination centers on the modulated photocurrent: Determination of the gap state parameters of semiconductors

“…Specifically, the Y spectrum is extracted from the DOS presented in Fig.24(a) of Ref. [24] which was calculated by means of the formula of Bruggenann et al [6]. This formula is equivalent to our Eq.…”

“…Based on this analysis Bruggemann et al [6] in 1990 proposed a formula for the determination of the so-called reduced DOS (r-DOS), (c/µ)D(E ω ). This formula provides by means of the i ac and φ data the r-DOS at the probe energy level E ω for which the thermal emission rate of the majority carriers equals the modulation frequency ω.…”

“…The output from the amplifier is analyzed by a Lock-in amplifier, which provides the amplitude, i ac , of the MPC and the phase shift, φ, between the MPC and the modulated light (see Fig.1(b)), which may be a phase lag [1,[5][6][7][8] or a small phase lead [15] . The theoretical analysis of the MPC data is based on the multiple trapping model and the derived basic expressions indicate two different regimes: that at high frequencies (ω) and/or low bias light levels, the so-called high frequency (HF) or emission-limited regime and that at low frequencies and/or high bias light levels, the so-called low frequency (LF) or trapping-limited regime.…”

“…The modulated photocurrent (MPC) technique has been applied to determine the density of states (DOS) in the energy gap of various semiconductors including crystalline [1][2][3], amorphous [4][5][6][7][8][9][10], microcrystalline [11], quasicrystalline [12] as well as organic [13,14] semiconductors. This technique is very powerful as it can reveal even very low trap densities, as well as the capture coefficients.…”

Sharp exponential band tails in highly disordered lead sulfide quantum dot arrays

“…The use of a lock-in amplifier to analyze the magnitude and phase shift of the AC photoresponse of a sample as a way to determine the sub-band gap DOS was first introduced by Oheda et al [44] and later refined by Brüggeman et al [45] and Hattori et al [46] The experiment is illustrated schematically in Fig. 1A.…”