Experimental performances and Monte Carlo modelling of LWIR HgCdTe avalanchephotodiodes

摘要

We report the performances of LWIR (X, = 9.0 pm at 80K) HgCdTe electron injectedavalanche photodiodes (e-APD). In these devices, the exponential gain curve, up to gainsequal to 23 at 100K, and the low excess noise factor close to unity (F 1-1.25) are indicativeof a single carrier multiplication process, which is electron impact ionization. The darkcurrent is mainly due to a diffusion current at low reverse bias and tunneling currents at highreverse bias. A Monte Carlo model has been developed for understanding the multiplicationprocess in Hgi_xCd,Te e-APDs. We find a good agreement between first simulation resultsand experimental measurements of the gain and the excess noise factor in both MWIR (x =0.3) and LWIR (x = 0.235) e-APDs at 80K. Furthermore, simulations do not show any heavyhole impact ionization. This model which enables to perform phenomenological studies aimsat identifying the main physical and technological parameters that influence the gain and theexcess noise. In the present work, it is used to study the influence of the thickness of the n-doped region on the gain and the excess noise factor. We found that F still decreases while thethickness of the n- layer decreases. However, an optimum thickness of the n- layer existsaround 1pm in terms of gain-voltage characteristic.