Research On Microstructure And Photoelectric Properties Of In InAs/GaSb Superlattice

InAs/GaSb type-II superlattice is considered as a valuable candidate for the third generation infrared detectors.Compared with HgCdTe bulk material,InAs/GaSb type-II superlattice has a lot of advantages,such as adjustable band gap,large effective mass and good uniformity.In theory,InAs/GaSb type-II superlattice infrared detector can achieve high quantum efficiency while maintaining high quantum efficiency.In the past decades,the research on InAs/GaSb type-II superlattice infrared detectors has been well developed.The presented results indicate that fundamental material issues of InAs/GaSb superlattice fulfill practical realization of high performance FPAs.However,the measured thermally limited detectivities of InAs/GaSb type-II superlattice detectors are as yet inferior to current HgCdTe photodiode performance.Their performance of superlattice detectors has not achieved theoretical values.This limitation can be attributed to many factors,such as,short minority carrier lifetime,interfacial intermixing and large dark current.In this dissertation,combined with superlattice interface control,the high quality InAs/GaSb superlattice materials have been grown by using MBE.The issues of strain control,interfacial intermixing and profile of vacancy point in InAs/GaSb superlattice have been systemic studied.Furthermore,very long wavelength InAs/GaSb superlattice infrared detectors with cutoff wavelength of 17?m have been prepared.And the main dark current mechanism of the p-i-n photodiodes also has been studied.The details are as follows:InAs/GaSb superlattices with different thickness of In Sb interface layer have been grown by using MEE method.The effects of the thickness of In Sb interface layer on strain balance,interfacial roughness and surface morphology have been studied.Empirical relationship between the thickness of In Sb layer and InAs layer in strain-balanced SL has been obtained: t In Sb=0.07 t InAs-0.21(ML).The interfacial structure of InAs/GaSb superlattices has been investigated by using high-resolution transmission electron microscopy(HRTEM).The results indicate that the as grown InAs/GaSb superlattices have smooth interface,uniform period thickness and few dislocations.Interface type and location jointly determine the interface bond configuration in InAs/GaSb superlattices.It is found that the In Sb bond configurations are different between InAs-on-Ga Sb and Ga Sb-on-InAs interface.The profile of vacancy point defects in InAs/GaSb superlattice have been studied by using Dopper broadening on slow position annihilation technology.It is found that the concentration of vacancy point defects in InAs/GaSb superlattice will increase as the content of Ga Sb increasing.The main type of vacancy point defects in InAs/GaSb superlattice is VGa which is the same as that in Ga Sb substrate.The profile of compositions in InAs/GaSb superlattice have been given by using the method combined HRTEM and DF-TEM.And then,S function and Muraki's segregation model were used to quantitative analyze the interfacial atomic intermixing and segregation in InAs/GaSb superlattice.It is found that the InAs-on-Ga Sb interface is wider than Ga Sb-on-InAs interface in InAs/GaSb superlattice.As/Sb exchange and Sb segregation primarily occur at InAs-on-Ga Sb interface,while In segregation occurs at Ga Sb-on-InAs interface.The effect of rapid thermal annealing on interface atomic intermixing of InAs/GaSb superlattice has been investigated.It is found that the As/Sb exchange will be important when RTA temperature below 480 ?,while In/Ga exchange will be activated when RTA temperature is over 500 ?.The superlattice infrared detectors with p-i-n type have been prepared.It shows that the cutoff wavelength and 50% cutoff wavelength of the detector is 17.1 ?m and 13.3 ?m,respectively.The peak responsivity of the devices under zero bias is about 0.67 A/W at 11.3 ?m,giving the external quantum efficiency(?)of 6.3 %.The measured value of the dynamic impedance area at zero bias(R0A)for the device with the mesa size of 400×400 ?m2 was 0.0173 ?cm2 at 77 K which leads to a Johnson noise detectivity of 1.35×109 cm Hz1/2W-1.The quantum efficiency of InAs/GaSb superlattice detector was investigated by using Hovel model.It is found that the short diffusion length of minority carrier in the intrinsic region is the main reason of the low quantum efficiency.Theoretical analysis shows that the quantum efficiency can be improved by doping Be in the intrinsic region.The dominant dark current mechanism in the very long wavelength InAs/GaSb superlattice infrared photodiodes at different temperatures have been studied by fitting the I-V characteristic curve.It is found that the dominant dark current mechanism at 45-90 K is the surface leakage current,while the diffusion dark current will be dominant when temperature over 100 K.