Switching characteristics as well as pre-breakdown characteristics were investigated in thin film of an amorphous semiconductor having the composition of As
30-Te
48-Ge
10-Si
12. Sandwich type samples with electron-blocking Au and electron-injecting Al electrodes were mainly used for the experiment. It was found that both electrodes play an important role for conduction in the pre-breakdown state and for switching phenomena.
A model was proposed for the switching mechanism, which also includes pre-breakdown carrier transport mechanism. According to the model, in the pre-breakdown state, electrical conduction is predominantly a one-carrier, space charge limited current caused by injected electrons, while injection of holes could not be observed. When the electron space charge density in the film reaches a critical value, however, hole injection begins and this causes switching action.
From the view point of this model, threshold voltage, threshold current, delay time before switching and stored charge density of electron are evaluated as function of geometrical factors such as film thickness or electrode area. It was concluded that the model proposed here satisfactorily explains several features of the switching characteristics in thin film of an amorphous semiconductor.
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