Performance of gas source MBE-grown wavelength-extended InGaAs photodetectors with different buffer structures

Wavelength-extended InyGa1−yAs photodiodes with cut-off wavelengths of 2.0, 2.4 and 2.7 μm at room temperature were grown using gas source molecular beam epitaxy with linearly graded InxAl1−xAs (x=0.52 to y) buffer layers and InyAl1−yAs cap layers. A convenient and reliable correlating ramping procedure was developed for the growth. Detector performances were compared with our standard homojunction detectors containing linearly graded InxGa1−xAs buffer layers. The heterojunction detectors showed better performance than the homojunction detectors. Also, the use of wider bandgap buffer and cap made the heterojunction detectors more suitable for both front and back illumination. For the photodiodes with 500 μm mesa diameter at room temperature, the typical dark current (VR=10 mV) and R0A were 74 nA and 104 Ω cm2 at 290 K for the cut-off wavelength of 2.4 μm. Optimization of the buffer structure was necessary for further extension of the response wavelength.