Investigation into MIS structures based on gradedband-gap hetero-epitaxial HgCdTe grown by molecular-beam epitaxy using photo-emf and conductivity methods

Abstract

621.315The effect of graded-band-gap layers on the differential resistance of space-charge region in MIS structures based on MBE HgCdTe (x = 0.225) is examined. It is shown that the effect of resistance of the epitaxial-film bulk on the measured capacitance and resistance should be taken into account for correct determination of space-charge region parameters. The presence of near-surface layers with increased Cd contents results in an increase in the resistance of the space-charge region in strong inversion. The product of semiconductor resistance by area as high as 15 Ω⋅cm 2 is obtained despite suppression of tunnel generation-recombination through deep levels in MIS structures with graded-band-gap layers. This might be due to background photogeneration and diffusion of minority charge carriers. The mechanisms for limitation of the differential resistance of space-charge region at different temperatures are discussed for n-HgCdTe (x = 0.225 and 0.292) and p-HgCdTe (x = 0.225). IN RODUCTIONMolecular-beam epitaxy (MBE) of Hg 1-x Cd x Te allows growing hetero-epitaxial structures with the specified indepth distribution of composition, which in turn makes it possible to further optimize the characteristics of infrared detectors. Near-surface layers with enhanced content of Cd decrease the effect of surface recombination on the chargecarrier lifetime in the epitaxial film bulk [1]. Examination of electrical characteristics of MIS structures based on graded-band-gap MBE HgCdTe is necessary for evaluation of the quality of passivating coatings as well as for development of monolithic IR detector arrays. The conventional methods for studying electrical characteristics of MIS structures are designed for semiconductors uniform in depth and cannot be applied to characterization of MIS structures based on graded-band-gap semiconductors in the same form. When examining the properties of MIS structures based on graded-band-gap MBE HgCdTe, one should take into account the resistance of epitaxial film bulk [2] and near-surface graded-band-gap layers [3]. The conductance of MIS structures in strong inversion provides information on the differential resistance of space-charge region (SCR) which determines the rate of recombination of minority carriers in the SCR. The product of the SCR differential resistance and the area (R SCR A d ) is the most important characteristic of MIS photodiodes [4,5] as well as photodiodes where the p-n transition is generated by doping [6,7]. Thus, in [4], for bulk HgCdTe of composition 0.22 the maximum value of those cited in literature R SCR A d = 120 Ω⋅cm 2 at 77 K is listed, whereas in [8], for epitaxial HgCdTe with composition 0.223 without a near-surface graded-band-gap layer, the values

Photoelectrical characteristics of metal–insulator–semiconductor structures based on graded-gap HgCdTe grown by molecular-beam epitaxy

“…where |U pe | is the modulus of the photo-emf, ReU pe and ImU pe are the real and imaginary components of the photo-emf, respectively, I p ¼ qη λ P hv , where q is the electron charge, η λ is the quantum efficiency, hv is the photon radiation energy, P is the optical power absorbed in the MIS structure, τ = R scr C scr , R scr and C scr are the resistance and capacitance of space charge region, respectively [34,35]. The resistance of SCR is associated with the current generation of minority carriers by the relation [35]: R scr ¼ kT q J p A d , where k is the Boltzmann constant, T is the temperature, q is the electron charge, J p is the density of the current generation of minority carriers, and A d is the area of the MIS structure electrode.…”

Influence of composition of the near-surface graded-gap layer on the admittance of metal-insulator-semiconductor structures based on graded-gap MBE n-Hg1−xCdxTe in wide temperature range

“…The values of the capacitance (C 1 ) and resistance (R 1 ) of the near−surface layer of the semiconduc− tor [the equivalent circuit in Fig. 2(c)] are given by the fol− lowing expressions [20] Note that under the condition R bulk = 0, Eqs. The equivalent circuit of the MIS structure in inversion mode takes the form shown in Fig.…”

“…Given values of the capacitance and resistance of the near−surface semiconductor layer we can calculate the mea− sured capacitance and resistance of the MIS structure with allowance for the influence of the bulk resistance using the following equations [20] Influence of composition of the near−surface graded−gap layer on the admittance of metal−insulator−semiconductor... …”

Admittance in MIS Structures Based on Graded-GAP MBE p-Hg1–х Cd х Te (x = 0.22–0.23) in the Strong Inversion Mode

“…The capacitance (C 1 ) and resistance (R 1 ) of this surface layer of the semiconductor (the equivalent circuit in Fig. 2c) were found using the following expressions [24]: …”

“…The measured capacitance and resistance of the MIS structure can be calculated by the following formulas using the known values of the capacitance and resistance of the near-surface semiconductor layer with allowance for the bulk resistance [24]:…”