Abstract
We designed and demonstrated an InAs avalanche photodiode (APD) for X-ray detection, combining narrow band gap semiconductor materials and avalanche gain from APDs. The InAs APD (cooled by liquid nitrogen) was tested with a 55Fe X-ray source. Full width at half maximum (FWHM) from the spectra decreases rapidly with reverse bias, rising again for higher voltages, resulting in a minimum FWHM value of 401 eV at 5.9 keV. This minimum value was achieved at 10 V reverse bias, which corresponds to an avalanche gain of 11. The dependence of FWHM on reverse bias observed is explained by the competition between various factors, such as leakage current, capacitance and avalanche gain from the APD, as well as measurement system noise. The minimum FWHM achieved is largely dominated by the measurement system noise and APD leakage current.
Highlights
We designed and demonstrated an InAs avalanche photodiode (APD) for X-ray detection, combining narrow band gap semiconductor materials and avalanche gain from APDs
We previously reported an InAs APD with an n-i-p structure for X-ray detection [17]
We report the soft X-ray detection performance of InAs APDs with p-i-n structure
Summary
The InAs APDs were fabricated from an InAs p-i-n diode wafer grown on a 2” n-type InAs substrate by molecular beam epitaxy. The 75 μm diameter diodes, whose top view is shown, offered the best trade-off between minimizing capacitance and maximizing the sensitive area for X-ray detection. X-ray data presented later were obtained from diodes with 75 μm diameter, which were wire-bonded onto TO-5 packages to facilitate low temperature X-ray measurements. Prior to X-ray measurements, reverse leakage currents of D1 and D2 were measured at room temperature, as shown in figure 2(a). Comparison with on-wafer measurement data indicates degradation in leakage currents caused by the packaging process. Cooling the device to 77 K reduces the bulk leakage current significantly [19], shown, making the detection of X-rays possible. On-wafer Capacitance-Voltage dependence of the 75 μm diameter InAs APD at 77 K, plotted in figure 2(b), shows that the capacitance decreased rapidly with reverse bias voltage from zero to 4 V, but remains relatively unchanged for higher reverse bias (0.18 pF at 10 V)
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