8 Search Results

The minority carrier lifetime (τMC) and equilibrium electron concentration (i.e., the doping level, n0) are both important values that directly determine diffusion current in infrared photodetectors utilizing n-type absorbing regions. Here, time-resolved microwave reflectance measurements are used to non-destructively measure both of these values in mid-wave infrared InAs/InAs1−xSbx type-II superlattices with varying n-type doping levels between 2×1014 cm−3 and 2×1016 cm−3. The measured data are analyzed using carrier recombination theory to determine the doping level ranges where Shockley-Read-Hall (SRH), radiative, and Auger recombination limit τMC. The optimal doping level, which minimizes dark current, is experimentally determined and corresponds to themore » electron density at which τMC switches from SRH limited to Auger limited behavior. A comparison of two InAs/InAs1−xSbx photodetectors of different equilibrium electron densities demonstrates a decrease in dark current for a doping level near the optimal n0τMC product.« less

Measurements of the equilibrium majority carrier electron concentration (n0) in narrow-bandgap n-type InAs/InAs1−xSbx type-II superlattices are made using contactless time-resolved microwave reflectance (TMR). By calibrating TMR decays to the number of optically injected electron-hole pairs, direct conversion to carrier lifetimes as a function of excited carrier density is made and allowing for accurate measurement of n0. The temperature dependence of both n0 and the intrinsic carrier density (ni) are measured using this method, where n0 = 1 × 1015 cm−3 and ni = 1.74 × 1011 cm−3 at 100 K. These results provide non-destructive insight into critical parameters that directly determine infrared photodetector dark diffusion current.

Optical and electrical properties of nBn photodetectors using InAs/AlAs/AlSb/AlAs/InAs/InAs0.61Sb0.39W-structure superlattice (W-SL) absorbers are reported. Minority carrier lifetimes of 500 ± 50 ns and 400 ± 30 ns, and Auger coefficients of 2.1 × 10−26 cm6/s and 1.6 × 10−25 cm6/s, for samples with bandgap energies of 5.3 μm (W-SL A) and 7.5 μm (W-SL B) are reported at 100 K, respectively. Shockley–Read–Hall defect states are identified at 65 meV and 45 meV above the W-SL valence band edges for W-SLs A and B, respectively. Dark currents are also reported and compared with diffusion currents calculated using the carrier lifetime data, suggesting low vertical heavy hole diffusivity.

Direct current (DC) transport and far infrared photoresponse were studied an InAs/GaSb double quantum well with an inverted band structure. The DC transport depends systematically upon the DC bias configuration and operating temperature. Surprisingly, it reveals robust edge conduction despite prevalent bulk transport in our device of macroscopic size. Under 180 GHz far infrared illumination at oblique incidence, we measured a strong photovoltaic response. We conclude that quantum spin Hall edge transport produces the observed transverse photovoltages. Overall, our experimental results support a hypothesis that the photoresponse arises from direct coupling of the incident radiation field to edge states.

The Auger lifetime is a critical intrinsic parameter for infrared photodetectors as it determines the longest potential minority carrier lifetime and consequently the fundamental limitations to their performance. Here, Auger recombination is characterized in a long-wave infrared InAs/InAsSb type-II superlattice. Auger coefficients as small as 7.1×10^–26 cm⁶/s are experimentally measured using carrier lifetime data at temperatures in the range of 20 K–80 K. The data are compared to Auger-1 coefficients predicted using a 14-band K•p electronic structure model and to coefficients calculated for HgCdTe of the same bandgap. In conclusion, the experimental superlattice Auger coefficients are found to be anmore » order-of-magnitude smaller than HgCdTe.« less

We present that temperature-dependent measurements of carrier recombination rates using a time-resolved optical pump-probe technique are reported for mid-wave infrared InAs/InAs_1-xSb_x type-2 superlattices (T2SLs). By engineering the layer widths and alloy compositions, a 16 K band-gap of ~235 ± 10 meV was achieved for five unintentionally and four intentionally doped T2SLs. Carrier lifetimes were determined by fitting lifetime models based on Shockley-Read-Hall (SRH), radiative, and Auger recombination processes to the temperature and excess carrier density dependent data. The minority carrier (MC), radiative, and Auger lifetimes were observed to generally increase with increasing antimony content and decreasing layer thickness for themore » unintentionally doped T2SLs. The MC lifetime is limited by SRH processes at temperatures below 200 K in the unintentionally doped T2SLs. The extracted SRH defect energy levels were found to be near mid-bandgap. Additionally, it is observed that the MC lifetime is limited by Auger recombination in the intentionally doped T2SLs with doping levels greater than n ~10¹⁶ cm^-3.« less

Carrier lifetime and dark current measurements are reported for a mid-wavelength infrared InAs _0.91Sb_0.09 alloy nBn photodetector. Minority carrier lifetimes are measured using a non-contact time-resolved microwave technique on unprocessed portions of the nBn wafer and the Auger recombination Bloch function parameter is determined to be |F₁F₂|=0.292. Moreover, the measured lifetimes are also used to calculate the expected diffusion dark current of the nBn devices and are compared with the experimental dark current measured in processed photodetector pixels from the same wafer. As a result, excellent agreement is found between the two, highlighting the important relationship between lifetimes and diffusionmore » currents in nBn photodetectors.« less