Effect of long-term He–Ne laser light exposure and subsequent annealing on hydrogenated amorphous silicon pin photodiodes

Abstract

Changes in the current–voltage (IV) characteristics were monitored on as prepared a-Si:H pin photodiodes during 60 min He–Ne laser illumination (every 15 min in situ measurements). After illumination was over, the pin diodes were subjected to 1 h annealing at 200 °C and IVs were taken again. Results showed that the short circuit current (Isc) decreased with the He–Ne exposure time which is known as a Stabler–Wronski effect of degradation and increased after the annealing. In order to describe the origin of this phenomenon, a 1 µm thick a-Si:H film was deposited on Mo-coated glass sheets by plasma enhanced chemical vapour deposition (PECVD) using the same procedure as that of the i-type layer in the pin diodes. Fourier transform infrared spectra (FTIR) were taken on the sample before and after the 1 h He–Ne laser exposure as well as after annealing for 1 h at 200 °C in air. Hydrogen (H) concentration in the film was estimated from the typical Si–H vibration absorbance peak at 2000 cm−1. The results showed that the H-concentration decreases from the initial value of about 10%, to about 7% after the 1 h He–Ne laser exposure. After the thermal annealing, the hydrogen concentration increased to about 9%. The above hydrogen concentration change was directly related to the change in the IV characteristics of the pin a-Si:H diode.