We characterize the phototransistor internal gain of metamorphic high-electron-mobility transistors ͑mHEMTs͒. When the mHEMT operates as a phototransistor, it has internal gain provided by the photovoltaic effect. To determine this internal gain, photoresponse characteristics dominated by the photoconductive effect as well as the photovoltaic effect are investigated. When the device is turned off, it acts as a photoconductor, and by calculating photoconductor gain, the primary photodetected power can be determined, which indicates the absorbed optical power. The ratio between this and the photodetected power due to the photovoltaic effect represents phototransistor internal gain. It is demonstrated that the phototransistor internal gain is function of optical modulation frequency.

The authors report silicon avalanche photodetectors ͑APDs͒ fabricated with 0.18 m standard complementary metal-oxide-semiconductor ͑CMOS͒ process without any process modification or a special substrate. When the bias is above the avalanche breakdown voltage, CMOS-compatible APD ͑CMOS-APD͒ exhibits negative photoconductance in photocurrent-voltage relationship and rf peaking in the photodetection frequency response. The reflection coefficient measurement of CMOS-APD indicates that rf peaking is due to resonance caused by appearance of inductive components in avalanche region. The rf-peaking frequency increases with the increasing reverse bias voltage.

An optical receiver using a CMOS-compatible avalanche photodetector (CMOS-APD) is demonstrated. The CMOS-APD is fabricated with 0.18 μm standard CMOS technology and the optical receiver is implemented by using the CMOS-APD and a transimpedance amplifier on a board. The optical receiver can detect 6.25-Gb/s data with the help of the series inductive peaking effect.

No abstract

No abstract