Fabrication and characterization of nbn Inas/Gasb/B-Al(x)ga(1-x)sb type-II superlattice detectors with dual-color detection in mwir

Çekmez, Utku
Type-II superlattice detectors with nBn structure made it possible to detect at higher temperatures due to the suppressing of the dark current components originating from Shockley-Read-Hall (SRH). In this context, the Al(x)Ga(1-x)Sb layer with wider band-gap energy was designed to act as an electron barrier between the n-doped N-Structure InAs/AlSb/GaSb type-II superlattice layers, whose active layers are capable of dual-color detection at mid-wavelength. In this thesis work, the fabrication processes of the growth design were carried out in pixel size. The test detectors with mesa form and different perimeter-to-area ratios (100×100, 150×150, 200×200, 300×300 μm^2) were acquired by making the etching optimization known as shallow etch (T1) and deep etch (T2) in METU-MEMS Center. The electrical and optical characterizations of the samples were completed by making the temperature-dependent dark current density measurements and the blackbody responsivity measurements. Keithley 2635B SMU was used in dark current density measurement, but since the lowest current value that can measure for the device is 10^-12 A, the dark current density values of the samples could not be measured properly at lower temperatures than 160 K. Therefore, the dark current density analysis of 300 μm pixels from T1 and T2 were done at 160 K. The minimum dark current levels were obtained as 7.32×10^-12 A and 4.74×10^-10 A at 0.25 V for the shallow etch and the deep etch, respectively. Although low-level dark current values were achieved at low voltage bias, the dark current levels of the samples were found as 1.85×10^-6 A and 1.44×10^-6 A for the shallow etch and the deep etch, respectively, at 2 V, which the high photoresponsivity exists for mid-wavelength. The differential-resistance × detector area (R0.A) at 0.25 V were calculated as 7.86×10^7 Ω.cm^2 for shallow etch and 2.02×10^5 Ω.cm^2 for deep etch. The measured spectral responsivity data sent by the manufacturer company of the structure was used between 3-5 μm wavelength range and 2 V voltage bias for optical calculation. The blackbody responsivity measurements of the samples were obtained at 800 K (λpeak=3.6 μm) with cavity blackbody. The peak responsivity values of the samples were found as 1.5 A/W and 0.46 A/W at the λpeak wavelength for the T1 and T2 using the photocurrents of the samples at 2 V voltage bias and spectral responsivity data. The external quantum efficiency and thermal noise limited specific detectivity of the samples were estimated 50% and 1.7×10^11 Jones for T1 and 15% and 5×10^10 Jones for T2. The dark noise values of the samples were calculated as theoretically by using the differential resistance values and the dark current values at 2 V. The thermal noise and the shot noise values were found as 1.63×10^-13 A/√Hz and 7.70×10^-13 A/√Hz for T1, 1.51×10^-13 A/√Hz and 6.79×10^-13 A/√Hz for T2.


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Citation Formats
U. Çekmez, “Fabrication and characterization of nbn Inas/Gasb/B-Al(x)ga(1-x)sb type-II superlattice detectors with dual-color detection in mwir,” M.S. - Master of Science, Middle East Technical University, 2022.