This paper has proposed the device that is composed of a hetrojunction phototransistor (HPT) and a laser diode (LD). The expressions describing the transient response of the output. The rise time, and the output derivative are derived. The effect of the various device parameters on the transient response is outlined. The results show that the transient response of these types of devices is strongly dependent on the optical feedback inside the device and it is found that the device works in two different modes, which are: amplification, for small optical feedback coefficient. Switching, for high optical feedback coefficient. The transient behavior of the integrated device is investigated by considering: i) the frequency response of a phototransistor and a light-emitting diode, and ii) the optical feedback inside the devices. The analytical expressions describing the transient response of the integrated device are derived, and the rise times in both the amplification and the switching modes also are calculated in order to calculate the transmission bit rates depend on non return to zero (NRZ) and return to zero (RZ) coding formats in both amplification and switching modes. By increasing the optical feedback, the rise time in the amplification mode is increased along with an increasing output, while that in the switching mode can be reduced effectively with a saturated output.
Key words: Dynamic characteristics, amplification and switching modes, heterojunction phototransistor (HPT), and irradiation environments
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