Raman and X-ray Photoemission Identification of Colloidal Metal Sulfides as Potential Secondary Phases in Nanocrystalline Cu 2 ZnSnS 4 Photovoltaic Absorbers

The aim of this study is to establish reliable spectroscopic fingerprints of compounds that may form as secondary phases in Cu2ZnSnS4 (CZTS) nanocrystals (NCs) synthesized by “green” colloidal chemistry directly in aqueous solutions or during post-processing of NC films for photovoltaic application. For this purpose, we investigated a series of binary and ternary compound NCs synthesized under the same conditions as the quaternary CZTS NCs. The capabilities of combined Raman and X-ray photoemission (XPS) spectroscopies are used to identify these compounds formed separately and define spectral fingerprints for distinguishing them as possible secondary phases in the spectra of CZTS NCs. Besides the conventional analysis of element ratios and chemical shifts of the core-level peaks in the XPS spectra, the careful analysis of Auger lines and modified Auger parameters are applied to distinguish otherwise similar spectral contributions of different compounds. In the case of CuxS NCs the binding energy separation between the Cu2p3/2 and S2p3/2 core-levels is used as the additional fingerprint. As a criterion of a certain crystal structure in Raman spectroscopy, we rely not only on frequency positions of particular phonon modes but also on selective probing of different compounds at different (resonant) excitation wavelengths. The reasons of controversial previous reports on Raman spectra of CuxS are revealed and characteristic Raman spectra of Sn-poor Cu-Sn-S and Sn-poor Zn-Sn-S are proposed. For Cu-Zn-S, a mixture of CuxS and ZnS is formed under the given mild conditions rather than ternary compounds or alloys

Enhanced recrystallization and dopant activation of P+ ion-implanted super-thin Ge layers by RF hydrogen plasma treatment

Radio-frequency (RF) hydrogen plasma treatment, thermal annealing in a furnace, and rapid thermal annealing of high-dose P+ ion implanted p-type Ge layers have been studied by Raman scattering spectroscopy, atomic force microscopy, secondary ion mass spectrometry, electrochemical capacitance-voltage profiling, four-point probes method, and x-ray reflectometry. It was shown that low-temperature RF plasma treatment at temperature about 200 degrees C resulted in full recrystallization of amorphous Ge layer implanted by P+ ions and activation of implanted impurity up to 6.5 x 10(19) cm(-3) with a maximum concentration at the depth of about 20 nm. Rapid thermal annealing (15 s) and thermal annealing (10 min) in nitrogen ambient required considerably higher temperatures for the recrystallization and activation processes that resulted in diffusion of implanted impurity inside the Ge bulk. It was demonstrated that RF plasma treatment from the samples with front (implanted) side resulted in considerable stronger effects of recrystallization and activation as compared with the same treatment from the back (unimplanted) side. The experiment shows that nonthermal processes play an important role in enhanced recrystallization and dopant activation during the RF plasma treatment. Mechanisms of enhanced modification of the subsurface implanted Ge layer under plasma treatment are analyzed. (C) 2017 American Vacuum Society