Doping is one of the most important issues in semiconductor physics. In many cases, when people describe carrier concentration as a function of dopant density and Fermi energy, they usually assume only one type of dopant with single transition energy level in the system. However, in reality, the situation is often more complicated, that is, in a semiconductor device, it usually contains multidopants and each can have multitransition energy levels. In this paper, using detailed balance theory and first-principles calculated defect formation energies and transition energy levels, we derive formulas to calculate carrier density for semiconductor with multidopants and multitransition energy levels. As an example, we studied CdTe doped with Cu, in which V Cd , Cu Cd , and Cu i are the dominant defects/impurities. We show that in this system, when Cu concentration increases, the doping properties of the system can change from a poor p-type, to a poorer p-type, to a better p-type, and then to poor p-type again, in good agreement with experimental observations.

Recombination is critically limiting in CdTe devices such as solar cells and detectors, with much of it occurring at or near the surface. In this work, we explore different routes to passivate p-type CdTe surfaces without any intentional extrinsic passivation layers. To provide deeper insight into the passivation routes, we uniquely correlate a set of characterization methods: surface analysis and time-resolved spectroscopy. We study two model systems: nominally undoped single crystals and large-grain polycrystalline films. We examine several strategies to reduce surface recombination velocity. First, we study the effects of removing surface contaminants while maintaining a near-stoichiometric surface. Then we examine stoichiometric thermally reconstructed surfaces. We also investigate the effects of shifting the surface stoichiometry by both “subtractive” (wet chemical etches) and “additive” (ampoule anneals and epitaxial growth) means. We consistently find for a variety of methods that a highly ordered stoichiometric to Cd-rich surface shows a significant reduction in surface recombination, whereas a Te-rich surface has high recombination and propose a mechanism to explain this. While as-received single crystals and as-deposited polycrystalline films have surface recombination velocities in the range of 105–106 cm/s, we find that several routes can reduce surface recombination velocities to <2.5 × 104 cm/s.

CdTe is one of the most promising materials for thin-film solar cells. However, further improvement of its performance is hindered by its relatively short minority-carrier lifetime. Combining theoretical calculations and experimental measurements, we find that for both intrinsic CdTe and CdTe solar cell devices, longer minority-carrier lifetimes can be achieved under Cd-rich conditions, in contrast to the previous belief that Te-rich conditions are more beneficial. First-principles calculations suggest that the dominant recombination centers limiting the minority-carrier lifetime are the Te antisite and Te interstitial. Therefore, we propose that to optimize the solar cell performance, extrinsic p-type doping (e.g., N, P, or As substitution on Te sites) in CdTe under Cd-rich conditions should be a good approach to simultaneously increase both the minority-carrier lifetime and hole concentration.

Using a first-principles method, we investigate the structural and electronic properties of grain boundaries (GBs) in polycrystalline CdTe and the effects of copassivation of elements with far distinct electronegativities. Of the two types of GBs studied in this Letter, we find that the Cd core is less harmful to the carrier transport, but is difficult to passivate with impurities such as Cl and Cu, whereas the Te core creates a high defect density below the conduction band minimum, but all these levels can be removed by copassivation of Cl and Cu. Our analysis indicates that for most polycrystalline systems copassivation or multipassivation is required to passivate the GBs.

We have fabricated nitrogen-doped zinc oxide (ZnO) films that demonstrate p-type behavior by using metalorganic chemical vapor deposition. In our experiment, diethylzinc is used as a Zn precursor, and NO gas is used to supply both O and N to form a N-doped ZnO (ZnO:N) film. With these precursors, we have routinely reached an N concentration in the ZnO films of about 1–3 at. %. When the N concentration level is higher than 2 at. %, the films demonstrate p-type characteristics. The carrier concentration of the films varies from 1.0×1015 to 1.0×1018 cm−3, and mobilities are mainly in the 10−1 cm2 V−1 s−1 range. The lowest film resistivity achieved is ∼20 Ω cm.