Abstract:

We optimize the structure and parameters of the punchthrough enhanced phototransistor. We change the structure from traditional form, which is the combination of a NB (Narrow Base) punchthrough transistor and a WB (Wide Base) phototransistor to just one side, to a new shape of the narrow base punchthrough transistor sandwiched in two wide base phototransistors which are both half of the old length. We investigate the electrical properties and optical conversion performance of the device such as dark current, photocurrent and optical sensitivity versus bias voltage with different width of the narrow base region. The optimized width of the narrow base is obtained after we analyze the simulated result. The analysis of the photocurrent and optical sensitivity versus bias voltage with different light power are presented to reveal the character of different light power. When the width of the narrow base is 0.6 μm, the performance of the device is a optimum compromise. The dark current is only 1 μA when the bias voltage is 0.5 V. The optical sensitivity is 4×10⁶ A/W when the light power is 10^-7 W/cm².

Key words: punchthrough enhanced phototransistor, the width of the narrow base, dark current, photocurrent, optical sensitivity