Thin film heterojuctions of the type (n)ZnO/(p)CdTe with different doping concentration were prepared by vacuum evaporation, and their electrical and optical properties, both in dark and under illumination at room temperature as well as elevated temperatures, were studied. Different junction parameters such as ideality factors, barrier heights, Richardson constant, short-circuit current, etc. were determined from I–V characteristics. These parameters were found to change significantly on hydrogenation and annealing of the junctions and also on variation of temperature. The structures showed the change of the photovoltaic (PV) effect, giving a fill factor of 0.57 for hydrogen (H)-treated with an open-circuit voltage of 345 mV and a short-circuit current density of 75.72× 10−4 mA·cm−2 and 0.42 for untreated with an open-circuit voltage of 244 mV and a short-circuit current density of 52.00× 10−4 mA·cm−2 for doping concentrations of N
 a=2.43× 1016/cm3(2.53% Sb doped CdTe) and N
 d=3.88× 1015/cm3(2.74% Al doped ZnO). The junctions were found to possess a series resistance as high as 437 Ω for an untreated sample and 95 Ω for H-treated samples even under illumination. Proper doping, annealing, and hydrogenation are necessary to reduce the series resistance so as to achieve an ideal solar cell.

Electrical and Optical Properties of (n)ZnO/(p)CdTe Heterojunction and Its Performance as a Photovoltaic Converter

Hydrogen passivation effects in undoped p-ZnTe single crystals were studied by photoluminescence (PL) and photoconductivity (PC) measurements. Samples were exposed to r.f. hydrogen plasma at for different durations. Before passivation PL peaks were observed at 2.06 eV, 1.47 eV, 1.33 eV and 1.06 eV. After 60 min of exposure, samples showed strong band edge green luminescence at 2.37 eV due to an exciton bound to a Cu acceptor. In PC studies the dark current decreased by a factor of 70 on passivation for 60 min. From the temperature dependence of PC gain, the minority carrier lifetime was found to go through a maximum of at 220 K before passivation. After 60 min of hydrogenation, remained constant at for and decreased for . The activation energies of have been determined and show marked changes on passivation for . Comparison between PL and PC studies showed that the deep acceptor level responsible for emission at 2.06 eV is passivated, giving rise to strong band edge emission at 2.37 eV, while emission due to the midgap impurity levels at 1.47, 1.33 and 1.05 eV remained unaffected. The thermal activation energies of PL peaks have also been determined and allow the construction of a defect energy level diagram for ZnTe.

https://iopscience.iop.org/article/10.1088/0268-1242/13/12/018/pdf

Photoluminescence and photoconductivity in hydrogen-passivated ZnTe

Optical parameters of chalcogenide glass multilayers with 12–15 nm modulation lengths prepared by thermal evaporation can be changed by laser irradiation. Photoluminescence sPLd studies were carried out on such nonirradiated and irradiated multilayered samples of $ a-Se / As_2S_3$ (sublayer thickness of a-Se is 4–5 nm for one set of samples and 1–2 nm for the other set. However $As_2S_3$ sublayer thickness is 11–12 nm for both sets of samples.) PL intensity can be increased by several orders of magnitude by reducing the Se well layer slower band gapd thickness and can be further increased by irradiating the samples with appropriate wavelengths in the range of the absorption edge. The broadening of luminescence bands takes place either with a decrease in Se layer thickness or with irradiation. The former is due to the change in interface roughness and defects because of the enhanced structural disorder while the latter is due to photoinduced interdiffusion. The photoinduced interdiffusion creates defects at the interface between Se and $As_2S_3$ by forming an As–Se–S solid solution. From the deconvoluted PL spectrum, it is shown that the peak PL intensity, full width half maximum, and the PL quantum efficiency of particular defects giving rise to PL, can be tuned by changing the sublayer thickness or by interdiffusion.

Enhancement of photoluminescence intensity by photoinduced interdiffusion in nanolayered a-Se∕As2S3 films

A method of manufacturing a thin film photovoltaic device includes depositing a first compound semiconductor layer on a substrate and exposing the device to plasma, the plasma treating the layer.

Plasma-treated photovoltaic devices

This chapter discusses surface and interfacial recombination in semiconductors. If a semiconductor surface has defects such as vacancies, it creates dangling bonds. These vacancies have energies in the bandgap of the semiconductor. Foreign impurity atoms also have midgap energies. These trap states participate in nonradiative recombination with electrons and holes. The nonradiative recombinations have detrimental effects on both the performance and the shelf life of the semiconductor device. This chapter discusses the Fermi level pinning because of surface states, and provides the theoretical basis for the surface and interface recombination in semiconductors. There are tremendous opportunities now to understand the electronic structure of semiconductor surfaces by advanced laser techniques. Surface and interface recombination is very significant in semiconductor technology. Surface-passivation methods are useful in controlling the surface Fermi level. Future technologies should make it possible to achieve extremely pure semiconductor surfaces that are necessary for ultralarge-scale integration (ULSI) technology.

Chapter 3 – SURFACE AND INTERFACIAL RECOMBINATION IN SEMICONDUCTORS

Passivation effects in In doped n-CdTe upon exposure to rf hydrogen plasma are studied by electrical and photoluminescence measurements and were found to be maximum at about 150°C. Depth profiling by capacitance-voltage measurements show passivation of approximately an order of magnitude at 150°C and 50% at 170°C. No visual surface damage is seen. Reverse bias annealing experiments show that atomic hydrogen drifts in a charged state in n-CdTe, with reactivation kinetics of the donors different from the other well studied semiconductors. Manifestation of the donor passivation in photoluminescence is seen by the reduction of the donor bound luminescence.

Shallow donor neutralization in CdTe:In by atomic hydrogen

The inherent metallurgical problems associated with the HgTe/CdTe pseudobinary alloy system render the standard crystal growth processes inapplicable to the preparation of mercury cadmium telluride crystals for infrared detector applications. A variety of rather nonconventional techniques have been developed to overcome these problems. Two such techniques, viz. asymmetrical Bridgman and horizontal casting for solid-state recrystallization, developed at Solid State Physics Laboratory for the bulk growth of mercury cadmium telluride crystals are reviewed in this communication.

/pdf/some-recent-advances-in-bulk-growth-of-mercury-cadmium-3kqeno4em7.pdf

R. K. Bagai

Papers

Shallow donor neutralization in CdTe:In by atomic hydrogen

Some recent advances in bulk growth of mercury cadmium telluride crystals