Characterization of HgCdTe MWIR Back-Illuminated Electron-Initiated Avalanche Photodiodes

Abstract

This article reports new characterization data for large-area (250 lm · 250 lm) back-illuminated planar n-on-p HgCdTe electron-initiated avalanche photodiodes (e-APDs). These e-APDs were fabricated in p-type HgCdTe films grown by liquid-phase epitaxy (LPE) on CdZnTe substrates. We previously reported that these arrays exhibit gain that increases exponentially with reverse bias voltage, with gain-versus-bias curves that are quite uniform from element to element, and with a maximum gain of 648 at -11.7 V at 160 K for a cutoff wavelength of 4.06 lm. Here we report new data on these planar e-APDs. Data from a third LPE film with a longer cutoff wavelength (4.29 lm at 160 K) supports the exponential dependence of gain on cutoff wavelength, for the same bias voltage, that we reported for the first two films (with cutoffs of 3.54 lm and 4.06 lm at 160 K), in agreement with BeckÕs empirical model for gain versus voltage and cutoff wavelength in HgCdTe e-APDs. Our lowest gain-normalized current density at 80 K and zero field-of-view is 0.3 lA/cm 2 at -10.0 V for a cutoff of 4.23 lm at 80 K. We report data for the temperature dependence of gain over 80 K to 200 K. We report, for the first time, the dependence of measured gain on junction area for widely spaced circular diodes with radii of 20 lm to 175 lm. We interpret the variation of measured gain with junction area in terms of an edge-enhanced electric field, and fit the data with a two-gain model having a lower interior gain and a higher edge gain. We report data for the excess noise factor F(M) near unity for gains up to 150 at 196 K. We describe the abrupt breakdown phenomenon seen in most of our devices at high reverse bias.

Latest Developments of HgCdTe e-APDs at CEA LETI-Minatec

“…The latter group has reported a gain-normalized dark current GNDC of 1 pA (GNDCD of 1.6 nA/cm 2 ) at T = 77 K and M = 10 in 250-lm square diodes with a cutoff wavelength of k c = 4.2 lm. 12 A lower value could be expected for the equivalent input current.…”

“…The lowest value of equivalent input current reported for this technology is about I eq_in = 7 fA, corresponding to a current density per pixel of J = 0.44 nA/cm 2 , estimated from a minimum value of NEPh min = 0.3 at a gain of M = 946. 11 The use of planar-type e-APD allows decorrelating the extension of the junction and the thickness of the absorption layer, to minimize the volume and the width of the junction to optimize the sensitivity by reducing the dark current generation. In addition, the response time can be reduced through a reduction of the collection time, by introducing a composition variation in the absorption layer that allows collecting the carriers through drift, and/or a reduction of the transit time, using a narrow multiplication layer.…”

A 2D Full-Band Monte Carlo Study of HgCdTe-Based Avalanche Photodiodes

“…HgCdTe-based avalanche photodetectors (APD) provide the best performance as they are characterized by high sensitivity and gain while exhibiting very low multiplication noise. [1][2][3] These features are intimately related to the material properties of HgCdTe alloys with cadmium concentrations below 53%. In fact, for these alloys, the impact ionization process is due almost exclusively to electrons, while holes do not contribute.…”

HgCdTe e-avalanche photodiode detector arrays

“…High gain with ultra low excess noise factor has been reported in MWIR HgCdTe e-APDs by several groups. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Results on design, fabrication and characterization of e-APD detector arrays using LPE grown p-HgCdTe epilayers are presented in this paper. Consideration of active cum passive modes of operation has been kept in mind in the development of these detector arrays.…”