Variable-area diode data analysis of surface and bulk effects in MWIR HgCdTe/CdTe/sapphire photodetectors

Abstract

This stJdy investigates the separate dark current components which are dom'nanr in the diffus'on-limited regime in MWIR n/p HgCdTe/CdTe/sapphire photodetectors. Both mesa and p.anar configurations of variable-area diodes were fabr:cated and evaluated over the temperatJre range from 78 to 250 K. Simple analytical express'ons are Jsed to calculate tne contributions of bulk, lateral and surface effects from the perimeterlarea aependence of R+l and measurement of the minority carr:er d:ffusion length. The analysis ind'cates that at 180 K the nesa diode results can oe accounted for oy bulk and lateral currents, but that the planar diodes are limiteo oy surface currents. The 780 r( median &A for the mesa jiodes ranges from 63 R cm2 for 500 x 500 pm2 d:ooe areas to 14 R cm2 for .30 x 30 pm2 aiodes at a cut-off wavelength of 4.64 pm. Scann'ng laser m'croscope neasuements determine the 180 K e ectron minority carrier diffus:on length to be 17-18um.

Small two-dimensional arrays of mid-wavelength infrared HgCdTe diodes fabricated by reactive ion etching-induced p-to-n-type conversion

“…A comparison of experimental results with the theoretical trends for diffusion (∼n i -2 ) and G-R (∼n i -1 ) currents shows that, at high temperatures, diffusion current dominates, whereas at lower temperatures, the G-R mechanism p-to-n type conversion of the underlying layer. 19,20 In this paper, we present a variable area diode analysis for devices with n-on-p junctions formed by RIE, and also report on the properties of small 8 × 8 test arrays to assess the yield and uniformity of the RIE based n-on-p junction technology. The physical mechanism for this type conversion is not fully understood, although it is generally accepted that the p-to-n conversion is related to migration of mercury atoms released during etching into the p-type HgCdTe layer.…”

Variable area MWIR diodes on HgCdTe/Si grown by molecular beam epitaxy

“…[8][9][10][11] To arrive at a general model applicable to a wide range of diode sizes and operating temperatures, we modified this to more explicitly include bulk diffusion, lateral diffusion, bulk generation-recombination (g-r), and surface g-r components, which are expected to be the main dark current mechanisms for MWIR diodes. The R 0 A measured is then given by:…”

Analysis of current voltage characteristics of MWIR homojunction photodiodes for uncooled operation

“…Increase of trap assisted tunneling via traps located at dislocation cores has been proposed as the mechanism of enhanced thermal generation of charge carriers in reverse biased diodes [3,8]. Variable area diode array (VADA) test structures are often used to evaluate contribution of surface leakage and tunneling currents to device performance using analytical equations that model the bulk diffusion and g-r terms, surface g-r and tunneling effects to zero bias resistance area product (R 0 A) through the constant term and coefficients of linear perimeter to area ratio (P/A) and quadratic (P/A) [2] terms respectively [9][10][11][12]. By making variable temperature measurements on VADA test devices and fitting the data with existing models one can get an insight about the relative contributions of fundamental bulk, g-r and tunneling contributions to the total dark current.…”