DEFECT FORMATION DURING DEPOSITION OF UNDOPED A-SI-H BY RF GLOW-DISCHARGE

Dependence of the as-grown defect concentration in undoped a-Si:H depo sited by rf glow discharge on the deposition parameters is investigate d. It is found that the defect density behaves similarly to the concen tration of SiH2 configuration in the films deposited at substrate temp eratures below 300 degrees C. The defect concentration varies proporti onally to about the third to fourth power of the SiH2 concentration de pending on the deposition conditions. The Urbach energy increases in s amples deposited under the condition where SiH2 concentration increase s. An additional energy is necessary to convert the weak bond in the v alence-band tail into the defect. The observed characteristics are ana lyzed by a model in which this additional energy is produced by the su rface reaction of SiH3 incorporating the SiH2 configuration into the n etwork. These characteristics are compared with those of the Staebler- Wronski effect. The increase of weak bond density contributes to the i ncrease of defect creation efficiency. The analyses give a quantitativ e explanation of the observed characteristics and estimation of some p arameters involved in the conversion process. Similarities in the mech anisms are pointed out between the as-deposited defect formation and t he Staebler-Wronski effect.