High frequency response of near-room temperature LWIR HgCdTe heterostructure photodiodes

The high frequency response of near-room temperature long wavelength infrared (LWIR) HgCdTe heterostructure photodiodes is investigated using a Fourier space method. The MOCVD HgCdTe multilayer heterostructures were grown on GaAs substrates. The response time of devices as a function of bias has been measured experimentally by using 10-μm quantum cascade laser and fast oscilloscope with suitable transimpedance amplifier. Results of theoretical predictions are compared with experimental data. It is shown that the response time at weak reverse bias condition is mainly limited by the drift time of carriers moving into π-n+ junction. Using the reverse bias higher than 50 mV, the transit time across the absorber region limits the response time. The response time of small-area devices decreases in the region of week reverse bias achieving value below 1 ns.