The Investigation Of InAs/GaSb Superlattice Photovoltaic Infrared Detector

InAs/Ga（In）Sb type-II superlattices has a special energy band structure whose energy gap isbetween that of InAs and GaSb. And we can adjust the energy gap according to the amount of In andthe ratio of InAs and GaSb. From this point, we can design the cutoff wavelength and make it have arange of2⁵0μm. And InAs/Ga（In）Sb type-II superlattices has many other advantages as smalleffective electron mass, long lifetime for carriers and a big absorb constant compared to otherinfrared detective material. So InAs/Ga（In）Sb type-II superlattices has a promising future in theinfrared detective field.This article investigates the theory and performance of InAs/GaSb superlattice infrared detector.The8bands k·p theory in envelope function approximation was introduced to calculate the energyband of this material and we give out the dependence of it to periods, the width of one period and theratio of width. When the period is between20to30, the cutoff wavelength increase as the adding toperiod. But we can’t see the same performance when the period is30to70. The increase of the InAsand width per period also make the cutoff wavelength longer.In order to test the performance of this material, I fabricated two PIN infrared detectorsaccording to the standard processing for fabrication of semiconductor. I have investigated two wetchemical etching system, tartaric acid and tartaric acid plus hydrochloric acid. In the liquid oftartaric acid system, HF act as a catalyst and the best option is0.4mL/400mL liquid. And theconcentration of H₂O₂can give a positive effect to the etching speed. But the H₂O₂also can destroythe shape of mask for it can oxidize photoresist. As the tartaric acid plus hydrochloric acid system, Igive the etching speed for InAs（56nm/Min）, GaSb（340nm/Min） and InAs/GaSb superlattices（96nm/Min and74nm/Min according to the width of InAs） under RT.After finish the fabrication, I-V test was introduced and we find that-J0=-2.3nA when V<-0.5V.And when-0.5V<Vbia<0.1V, the pn junction was dominated by Generation-Combine dark current.The negative bias can make the thermal created carriers separated and form current. So, it is thethermal generated dark current that dominated the dark current when bias voltage is in this range.The positive bias voltage can increase the carriers in the depletion area, so the chance forcombination of electrons and holes increase sharply. The C-V test can tell us that the open voltagesfor the two devices are0.5V and0.1V respectively. After the test of blackbody radiation and dark current test, we can calculate the inner quantumefficiency and the detectivities（D*） of the two devices. They are3.0×10¹⁴cmHz^1/2Wand1.5×10¹⁴cmHz^1/2W respectively under35K and under the assumption that all the photo energy radiated to thesurface of detector is absorbed without reflection.