Abstract
In this dissertation, we focus on the GaAs-based optical devices. It can be mainly divided into three parts. First of all, we have successfully fabricated and investigated the device performance in the heterojunction bipolar light-emitting transistor (HBLET). Second, we report the GaAs p-i-n structure, which is layer-compatible to the base-collector junction of a conventional InGaP-GaAs heterojunction bipolar transistor (HBT), is utilized in the fabrication of a PSD. Third, the multijunction solar cell consisting of III-V materials of InGaP/InGaAs/Ge has been investigated. At first, the common-emitter characteristics of the conventional HBT and HBLET are demonstrated. The peak value of common-emitter current gain β of the InGaP/GaAs HBT is close to 62 at 300K. On the other hand, the current gain of HBLET is in the range of 0.45-0.70, which is much smaller than that of HBT in the range of 30-65. For HBLET, the decrease of current gain is a trade-off to enhance light output power. The light output power increases linearly and achieves 0.58 mW at 50 mA and 1.09 mW at 110 mA. Due to the current applied to the base can modulate the light output power for HBLET; the current gain of HBLET is smaller than the conventional HBT. Second part, the GaAs-based p-i-n position sensitive detector are fabricated by conventional processes including photolithography, vacuum evaporation, and wet etching technique and investigated the device characteristic. It is possible that integrating a PSD with an HBT amplifier to design PSD circuits. In particular, sensitivity and linearity are two of most important sensing properties. Static sensing properties of the three-terminal PSD operated in lateral photovoltaic mode are performed using a light intensity of 3 mW and red light spot (the wavelength of 638 nm) to show a sensitivity of 14.3 mV/mm. Nonlinearities obtained from the present PSD are as small as 0.31.3% for 638 nm light sources. According to the model of photodiodes, the assumption that the total photocurrent produce two different directions photocurrent to catch in the PSD and interdiction of the 638 nm red light with an incident power of 2 mW. They are static characteristics of the fabricated PSD operated in lateral photovoltaic mode and transvere photovoltaic mode as well as response times. At last, the multijunction solar cells are formed by serially connecting multiple p-n junctions according to their energy-band gaps. Therefore the overall open-circuit voltage of the multijunction solar cell is equal to sum of individual open-circuit voltage associated with each subcell. However, the overall short-circuit current is limited by that of the subcell whose short-circuit is minimal. Our measurement system sets up for the nondestructive inspection of subcell’s short current. Destructive (using etching processes) and nondestructive inspection (using optical measurement) of subcell’s short circuit current were also discussed