Bandwidth characterization and optimization of high-performance mid-wavelength infrared HgCdTe e-avalanche photodiodes

Mid-wavelength infrared (MWIR) HgCdTe avalanche photodiodes (APD) have critical applications in the areas of sensing and imaging. However, most of the reports on HgCdTe have been focused on the DC characteristics such as the dark current, responsivity and gain. This work studied the frequency response of the MWIR HgCdTe APD, which is an important figure of merit for free space communication and dual frequency comb spectroscopy applications. The device with a 20 mu m diameter shows a low dark current of around 10-13A at low reverse bias, and achieves a gain up to 1356 under-11.4 V, along with a low excess noise of 1.3 at 78 K. The responsivity is about 1.48 A/W at 4.5 mu m wavelength under 0 V. The response bandwidth of the APD is about 635 MHz under-1 V. The device is characterized in detail to probe the limiting factors of the bandwidth. At last, an upside-down structure that enables APDs to realize higher gain-bandwidth products is proposed. It indicates that a bandwidth of more than 30 GHz can be realized with 1 mu m intrinsic region. Therefore, this investigation could offer a perspective on improving the bandwidth of HgCdTe APDs and advance the technology in free-space optical communication and other emerging areas.