HgCdTe electron avalanche photodiodes

Abstract

Exponential-gain values well in excess of 1,000 have been obtained in HgCdTe high-density, vertically integrated photodiode (HDVIP) avalanche photodiodes (APDs) with essentially zero excess noise. This phenomenon has been observed at temperatures in the range of 77-260 K for a variety of cutoff wavelengths in the mid-wavelength infrared (MWIR) band, with evidence of similar behavior in other IR bands. A theory for electron avalanche multiplication has been developed using density of states and electron-interaction matrix elements associated with the unique band structure of HgCdTe, with allowances being made for the relevant scattering mechanisms of both electrons and holes at these temperatures. This theory is used to develop an empirical model to fit the experimental data obtained at DRS Infrared Technologies. The functional dependence of gain on applied bias voltage is obtained by the use of one adjustable parameter relating electron energy to applied voltage. A more quantitative physical theory requires the use of Monte Carlo techniques incorporating the preceding scattering rates and ionization probabilities. This has been performed at the University of Texas at Austin, and preliminary data indicate good agreement with DRS models for both avalanche gain and excess noise as a function of applied bias. These data are discussed with a view to applications at a variety of wavelengths.

Recent progress in the development of MCT hot detectors

“…On the other hand, the data of our most advanced HOT-technology shows very little increase of the current between a typical operating bias of -200 mV and the maximum voltage of -3000 mV. Tentatively these characteristics can be compared to an empirical model describing avalanche multiplication first formulated by Beck [6] for MWIR and LWIR diodes, see (1) and (2). A cold shield kept at detector temperature limits the aperture to an F-number of 3.5.…”

Infrared Avalanche Photodiode Detectors

“…Asymmetry between effective mass of electron in the conduction band and heavy hole results in the unequal ionisation coefficient for electron and hole in HgCdTe material [25][26][27][28] . Electron mobility is two orders of magnitude higher than holes in HgCdTe due to their different scattering rates in HgCdTe.…”

“…On the other hand, at high electric field, the hot carriers gain sufficient energy (~E th ) from the field faster than they lose it and make possible to the impact ionisation process [28][29][30][31] . In HgCdTe material, low phonon scattering also results in the high gain with low noise 27 . Hg 1-x Cd x Te has a favorable impact ionisation ratio (k = α h / α e ) for different compositions from x = 0.1 to x = 0.7, where α h and α e are the ionisation coefficient for hole and electron, respectively.…”

“…The gain was uniform from element to element in an array. Kinch 27 , et al pioneered a theory, based on the band structure of HgCdTe, for explaining the unequal ionisation process of electron and hole in the avalanche phenomenon. Finally, it is concluded that electron-injection multiplication process is more favorable from SWIR to LWIR APD for achieving high gain at low reverse bias with low noise.…”

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.…”