Properties of R.F. sputtered CdS window layers and the performance of CdS/InP solar cells

Measurements of the electrical, optical, and structural properties of thin films of CdS used as window layers in conjunction with single-crystal InP and glass substrates are reported. RF-sputter deposition generally leads to films with a resistivity greater than 100,000 ohm cm. By cosputtering In, the resistivity can be reduced to about 100 ohm cm for a substrate temperature of 260 C. This is also the optimum temperature for optical and structural properties. Grain sizes in excess of 1 micron can be achieved. Efficiencies of about 7 percent have been achieved for solar cells using RF-sputter-deposited films of CdS on InP, and several obvious improvements are suggested. Damage to the extremely sensitive substrates does not appear to be the principal limitation, and the production of device-quality CdS by sputtering has been demonstrated.