ION- AND PHOTON-ASSISTED p-TYPE DOPING OF CdTe DURING PHYSICAL VAPOR DEPOSITION

Abstract

“Art jumps ahead – science plods ponderously on behind to consider, describe, and finally document what “;actually” happened in the chaos of the leap” (ALF)

This paper reviews our recent research on ion- and photon-assisted doping and growth of homoepitaxial CdTe thin films. Our earlier work demonstrated doping to 2 × 10¹⁷ cm⁻³ with 60 eVP ions during growth by vacuum deposition, but gave low values of minority-carrier diffusion length L_d. To increase Ld, we (a) explored photon-assisted doping, (b) varied the Cd/Te ratio, and (c) used lower ion energies. Although illumination (≈512 nm, ≈100 mW-cm⁻²) during growth enhanced crystalline quality, there was no evidence for any increase in doping over that of the non-illuminated films. Increasing the Cd/Te ratio (1.00 < Cd/Te < 2.2), both with and without ions and/or light during deposition, had strong effects on the In/p-CdTe junction transport, but gave little useful alteration of the doping behavior. Decreasing the P ion energy to 20 eV and adding an electron flux has thus far yielded substantially larger L_d with controlled doping up to 6 × 10¹⁶cm⁻³.

KEY WORDS:

• CdTe
• Doping
• II-VI semiconductors
• Ion-beam effects