Local redistribution of dopants and defects induced by annealing in polycrystalline compound semiconductors

Abstract

International audienceThe annealing of chlorine-doped polycrystalline CdTe films leads to the occurrence of an abnormal grain structure with the formation of both primary and secondary grains, the latter being larger and growing at the expense of the former. The spatial distribution of dopants and defects has been investigated within both types of grains by time-of-flight secondary-ion-mass spectroscopy imaging and spatially resolved cathodoluminescence. It is found that chlorine atoms similarly segregate in the vicinity of grain boundaries in both primary and secondary grains, whereas chlorine donors are homogeneously distributed away from grain boundaries. It is shown that, contrary to primary grains, secondary grains exhibit specific concentration processes around grain boundaries, such as cadmium vacancy accumulation and dislocation piling up. The existence of long-range stresses around grain boundaries only within secondary grains is also evidenced and attributed to piezoelectric effects. Grain boundaries thus act as getters for dopants and defects by draining them from the interior of secondary grains. These physical mechanisms emphasize efficient purifying effects associated with the beneficial formation and growth of secondary grains within an abnormal grain structure as induced by annealing. The depicted processes can be applied to a wide variety of polycrystalline compound semiconductors and can find direct applications in the field of solar cells based on these materials

A comprehensive picture of Cu doping in CdTe solar cells

“…It is also assumed that concentration of cadmium vacancies is thereby not increased, as V Cd also accumulate at grain boundaries. 23 According to the calculation of Du, 24 the diffusion barrier for Cd vacancies (V Cd ) and Cu Cd is similar, 1.08 eV and 1.03 eV, respectively.…”

Stability and electronic structure of the low-Σgrain boundaries in CdTe: a density functional study

“…They can exist in various forms and play important roles in determining material properties, and thus have been one of the most active research topics in materials science [1][2][3][4][5][6]. For example, segregation of impurities to the GBs is an effective way to purify materials, thus improving material quality for device applications [7][8][9][10][11][12]. GBs also increase phonon scattering, allowing the thermoelectric properties of a material to be improved by intentionally controlling its GB size [13,14].…”

Direct evidence of enhanced chlorine segregation at grain boundaries in polycrystalline CdTe thin films via three‐dimensional TOF‐SIMS imaging

“…For example, work by Emazine et al showed an approximately 100× increase in the chlorine concentration throughout the CdTe material after a CdCl 2 treatment . Several studies have provided evidence that chlorine segregates at grain boundaries in CdTe: imaging via Auger emission spectroscopy (AES) , as well as limited time‐of‐flight SIMS (TOF‐SIMS) imaging of enhanced chlorine concentration at grain boundaries on the surface of the CdTe material . To the authors' knowledge, the works by Consonni are the only applications of TOF‐SIMS imaging (with a lateral resolution superior to AES and dynamic SIMS) examining the spatial distribution of chlorine in CdTe after the CdCl 2 treatment.…”