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Defects in the band gap of CuIn1−xGaxSe2 have been characterized using transient photocapacitance spectroscopy. The measured spectra clearly show response from a band of defects centered around 0.8 eV from the valence band edge as well as an exponential distribution of band tail states. Despite Ga contents ranging from Ga/(In+Ga)=0.0 to 0.8, the defect bandwidth and its position relative to the valence band remain constant. This defect band may act as an important recombination center, contributing to the decrease in device efficiency with increasing Ga content.

Hydrogenated amorphous-silicon (a-Si:H) is grown by hot-wire chemical vapor deposition (HWCVD) at deposition rates (Rd) exceeding 140 A/s (∼0.8 μm/min). These high rates are achieved by using multiple filaments and deposition conditions different than those used to produce our standard 20 A/s material. With proper deposition parameter optimization, an AM1.5 photo-to-dark-conductivity ratio of 105 is maintained at an Rd up to 130 A/s, beyond which it decreases. In addition, the first saturated defect densities of high Rd a-Si:H films are presented. These saturated defected densities are similar to those of the best HWCVD films deposited at 5–8 A/s, and are invariant with Rd up to 130 A/s.

High-hydrogen-diluted films of hydrogenated amorphous Si (a-Si:H) 0.5 μm in thickness and optimized for solar cell efficiency and stability, are found to be partially microcrystalline (μc) if deposited directly on stainless steel (SS) substrates but are fully amorphous if a thin n layer of a-Si:H or μc-Si:H is first deposited on the SS. In these latter cases, partial microcrystallinity develops as the films are grown thicker (1.5–2.5 μm) and this is accompanied by sharp drops in solar cell open circuit voltage. For the fully amorphous films, x-ray diffraction (XRD) shows improved medium-range order compared to undiluted films and this correlates with better light stability. Capacitance profiling shows a decrease in deep defect density as growth proceeds further from the substrate, consistent with the XRD evidence of improved order for thicker films.

Voltage-pulse stimulated capacitance transient measurements on a series a-Si:H/a-Si, Ge:H devices disclose a large density of hole traps at or very close to the heterojunction interface. The transient signal magnitude is independent of temperature or applied bias, ruling out charge polarization effects or a defect creation process caused by the filling pulse. While the areal density of such hole traps is considerable (within a factor of 2 of 1011 cm−2 for all samples) these traps do not appear to behave as recombination centers. Also, the treatment of the a-Si:H/a-Si,Ge:H interface during growth can significantly alter the concentration of these traps.

We have applied transient photocapacitance and transient junction photocurrent measurements to the study of undoped hydrogenated amorphous silicon (a‐Si:H) films, and find that the electronic optical transition from the dominant deep defect is very similar in energy to the D−→D0+e optical transition identified in n‐type doped a:Si:H films. In addition, we have observed a competing hole thermal transition, and we have obtained estimates of its thermal emission rate and of the thermal gap. We have used the difference between photocapacitance and photocurrent in the valence‐band tail region to determine the quantity (μτ)hNT at different temperatures. Finally, we have observed that light‐induced metastable defects have a hole capture cross section significantly larger than that of the intrinsic defects.

We have observed a reversible photoinduced modification of the bulk density of gap states in a‐Si:H associated with the Staebler–Wronski effect. A detailed numerical analysis of diode admittance and deep level transient spectroscopy measurements shows that the changes in these properties after illumination can be explained by a lowering of the bulk Fermi level and an increase in the density of states below midgap.

We have developed a new method of capacitance profiling which is greatly superior to standard profiling techniques for materials like amorphous silicon that contain high densities of deep gap states. This technique, which makes use of the variation of the junction capacitance with the alternating voltage amplitude, is largely immune to the effects of surface states and is readily interpreted in terms of a simple integral over the density of states, g(E). This method is applicable to both doped and semi‐insulating undoped samples.

We have employed junction photocapacitance and thermal transient capacitance measurements in n‐type doped hydrogenated amorphous silicon and have identified, within each of a series of samples, the optical transitions: D−→D0+e and D0→D++e, and the thermal transitions: D−→D0+e and D+→D0+h, where D−, D0, and D+ denote the three charge states of Si dangling bond defect. We have also correlated the optical and thermal transitions associated with the valence bandtail states. Lattice relaxation energies are found to be less than 0.1 eV for the dangling bond transitions, but as large as 0.5–0.6 eV for the valence bandtail states. We also determined a value of Ueff for the D−/D0 splitting of 0.24±0.07 eV.