Device performance and current transport study of metal-induced grown microcrystalline Si for solar cell applications

Microcrystalline Si (μc-Si) thin films deposited at relatively low temperature by using the metal-induced growth (MIG) method have the potential for less metal impurity contamination and relative large grains with preferred crystal orientation in the <220> direction. Au/n-Si Schottky junction and P-N junction devices were fabricated using μ-Si films deposited under different process conditions. Electrical properties studied by using dark current (I-V), temperature dependence of current-voltage (I-V-T) and C-V analysis are important to reveal the current transport and understand the effects of the process conditions on the device performance. Single-stage sputtering Si deposition gave a Schottky junction device with a high degree of non-ideality and low barrier height. With a two-step sputtering process, in which the sputtering power and deposition rate were properly controlled, the device characteristics were largely improved since the Si grain size increased dramatically. Hydrogenation of the Si film by electron cyclotron resonance plasma treatment further improved the device characteristics in both ideality factor and barrier height. I-V-T testing revealed tunneling in current transport which was attributed to the high oxygen level and resulting thermal donor effect. By filtering the oxygen in the sputtering gas, the total charge state density was 3 times lower and tunneling was suppressed, especially in the high temperature region. Regarding the P-N junction devices, the similar I-V-T results implies that current transport in MIG μc-Si devices was mainly controlled by the bulk Si film instead of the device junction.