Atomic Imaging, Atomic Processing and Nanocharacterization of CuInSe2 Using Proximal Probe Techniques

Abstract

Defects play a dominant role in the determination of the electro-optical properties of single-crystal and polycrystalline CuInSe2. This paper examines the fundamental nature of point and grain boundary defects in this Cu-ternary semiconductor and, for the first time, provides direct evidence underlying the defect chemistry. Special scanning probe microscopy (SPM) techniques are used for real-time atomic imaging, atomic processing (single-atom manipulation), and nanoscale characterization of the same regions of the sample. The (220)-tri-elemental, p-rype surfaces are examined and imaged. Cu-, In-, and Se-vacancies are created using combined, pulsed electric (SPM tip-surface), and single-wavelength photon fields for selected, single-atom removal. The electro-optical characteristics of these defects (before and after creation) are examined using SPM-based nano-photoluminescence and nano-cathodoluminescence techniques that provide information in the same nanometer regime. Bulk photoluminescence spectra are compared and interpreted with respect to these data that give first time direct, atomic-level correlations. In addition, the healing of these point defects by the placement of single intrinsic atoms of the same type at the vacancy sites is accomplished using the atomic processing techniques. The electronic defect levels are verified and correlated with the atomic-scale observations. Finally, donor and acceptor defects, Cu and Se vacancies, Cu at In sites (CuIn) and Se at Cu sites (SeCu), are created, evaluated, and characterized. The placement of the acceptor heteroimpurity oxygen at Se vacancies is also examined. This is done both at isolated Se vacancies and at vacancies along electronically active grain boundaries. The passivation of these regions (by p-type doping of the grain boundary) is evaluated using nanoscale electron-beam induced-current (NEBIC), and newly-developed, SPM-based minority-carrier spectroscopy techniques. This paper reports, for the first time, the engineering of these defects on the atomic scale, and complements these results with the direct evaluation of the atomic manipulations using nanoscale electro-optical characterization methods.