Calculation of interface roughness scattering-limited vertical and horizontal mobilities in InAs/GaSb superlattices as a function of temperature

Abstract

Superlattice transport has acquired new relevance owing to the current interest in InAs/GaSb and other superlattices (SL) for third-generation infrared detector focal plane arrays. Interface-roughness scattering (IRS) is known to limit carrier mobilities at low temperatures. Whereas horizontal (in-plane) transport measurements are standard, perpendicular transport measurements (across SL layers)—the ones relevant to the operation of infrared sensors—are non-routine and seldom performed; vertical SL transport is also less well studied theoretically. Therefore, we extend our previous work on low-temperature SL transport by studying horizontal and vertical IRS-limited transport in InAs/GaSb SLs as a function of temperature, SL parameters, and the degree of roughness. Electron mobilities are calculated by solving the Boltzmann equation with temperature-dependent bands and carrier screening, and the results are discussed by analyzing the behavior of the relaxation rates and spectral mobilities, defined as mobilities as a function of carrier energy. New computational tools are devised to handle the implicit integral equation for the horizontal relaxation rates. We find that the behavior of the relaxation rates and spectral mobilities undergoes a change for energies below and above the conduction band bandwidth, which dictates the ultimate behavior of mobilities as a function of temperature. The calculated mobilities are found to display a rich variety of behaviors as a function of temperature, either increasing, decreasing, or remaining relatively constant, depending on the correlation length of interface roughness, Λ, and the conduction band bandwidth. Since the horizontal mobility is a double-valued function of Λ, the temperature dependence of mobilities can be used to eliminate this indeterminacy in order to assess the degree of interface roughness.

Midwave infrared InAs/GaSb superlattice photodiode with a dopant-free p–n junction

“…Despite these impressive progresses, experimental results on SL detectors have not yet reached their theoretical performances that are strongly dependent to their residual background carrier concentration. Consequently, fundamental studies on MWIR SL material, such as minority carrier lifetime [5][6][7], in plane and vertical effective masses [8] and mobilities [9,10], residual background carrier concentration [11][12][13], have been investigated for a better understanding of the carrier transport in this minority carrier detector. Recently, influence of the SL period thickness and composition on the electrical and optical properties of MWIR SL photodetectors has been reported [14].…”

Limiting dark current mechanisms in antimony-based superlattice infrared detectors for the long-wavelength infrared regime

“…For the electron and hole mobility we have chosen fixed numerical values of µ e = 2500 cm 2 /(Vs) and µ h = 300 cm 2 /(Vs) accounting for the strong localization of holes in InAs/GaSb SLs, which leads to low values of the vertical hole mobility [14]. The surface recombination velocities that we used were s 1 = 10 6 cm/s and s 2 = 0 cm/s reflecting the high conduction band offset at our GaSb:Be back contact for minority electrons.…”

Advancing carrier transport models for InAs/GaSb type-II superlattice MWIR photodetectors

“…Despite the fact that the mobility of the photogenerated minority carriers has a significant impact on the performance of IR photodetectors, carrier transport in technologically relevant T2SL structures has not as extensively been explored. Recent explorations in this context [17][18][19][20][21][22][23] which include carrier mobility calculations [24], do not conclusively bring to the fore structure-specific impact of important scattering mechanisms such as Piezoelectric (PZ), polar optical phonon (POP), acoustic deformation potential (ADP) scattering mechanisms and most importantly the interface roughness scattering (IRS).…”