Wednesday June 29, 2005
Thursday June 30, 2005

"Low-Temperature Grown GaAs based photodiodes for near-infrared wavelength operation"
Mr. Bayram Butun
Bilkent University

B. Butun, O. Aytur, Dept. of Electrical and Electronics Engineering, Bilkent University, Bilkent, Ankara 06800, Turkey E. Ozbay Dept. of Physics, Bilkent University, Bilkent, Ankara 06800, Turkey High-performance photodetectors operating in 1.3 - 1.6 µm wavelength range are vital components for long-haul optical fiber communication systems. Conventional GaAs-based photodetectors can only operate in the first optical communication window (λ~0.85 µm) due to low cut-off wavelength. It was shown that GaAs grown at low temperatures (LT-GaAs) was able to absorb long-wavelength signals due to midgap As defects and in addition it also exhibits sub-picosecond carrier trapping times. On the other hand, the long-wavelength absorption coefficient of LT-GaAs is much smaller than the interband absorption coefficient. This leads to poor efficiency performance with conventional single-pass vertical detector structures. To overcome the problem of low efficiency, a resonant cavity enhanced (RCE) detector structure is used. With this structure, the detector efficiency is selectively enhanced at the resonance wavelengths of the resonant cavity. In this work, we report the design, growth, fabrication, and characterization of GaAs-based high-speed p-i-n photodiodes operating at 1.55 μm. A LT-GaAs layer was used as the absorption layer and the photoresponse was selectively enhanced at 1.55 μm using a resonant cavity detector structure. The bottom mirror of the resonant cavity was formed by a highly reflective 15-pair GaAs/AlAs Bragg mirror. Molecular beam epitaxy was used for wafer growth, where the active LT-GaAs layer was grown at a substrate temperature of 200 °C. The fabricated devices exhibited resonance around 1548 nm. When compared to the efficiency of a conventional single-pass detector, an enhancement factor of 7.5 was achieved. Temporal pulse-response measurements were carried out at 1.55 μm. Fast pulse response with 30 ps pulse-width and a corresponding -3 dB bandwidth of 11.2 GHz was measured.