Research On Growth And Photoelectric Properties Of Type ? In As/GaSb Superlattice Materials

Due to the requirement of increasing the high performance of infrared detector,the photon detection because of the advantage in its high sensitivity,fast response,high detectivity,becomes the preferred material.With the progress of the molecular beam epitaxy technique?MBE?,type-? InAs/GaSb superlattice due to the band gap in the range of 3-30?m is tuned with high accuracy by adjusting the individual layers,can be large growth uniformity,has small tunneling current and high quantum efficiency,is expected to be a possible alternative to the state-of-the-art MCT technology in the 8-14?m even longer wavelength region,which has become an hot issue in research now.The type-? superlattice by optimizing the growth GaSb buffer layer,flux beam ?I/V ratio,interface type in combination with the migration enhanced epitaxy?MEE?technology has grown on the Ga Sb substrate.And subsequently,with improving the semiconductor fabrication processes,the unpassivated and passivated samples with different sizes were prepared for the study of mechanisms of dark currents and spectral response,which expect to improve the temperatures and detectivity by increasing the zero-bias voltage differential-resistence value.The details are as follows:The variation of the full width at half maximum?FWHM?for 0,±1 order SL diffraction peak and the surface roughness of the superlattice is investigated by changing the substrate temperatures are ranging from 390 to 420°C and the In Sb layer thickness of 0-2ML.As the growth temperature is reach 400°C and the In Sb layer thickness is 1 ML,it shows that the FWHM of the material is 24.84 arcsec and the surface roughness is 2?,which presents good material quality.It was also found that the photoluminescence?PL?peak appeared tiny red shift towards the longer wavelength at temperatures ranging from 4K to 77 K,which is similar to the bulk property.At 77 K,the band gap energy of the superlattice is shown to be 137.62 meV?9.01?m?.Transmission electron microscopy?TEM?shows that there is obvious interface between In As and Ga Sb layer,atomic lattice structure is visible and the thickness of the one period is obtained to be 6.4nm,which is consistent with the result of the high resolution X ray diffraction rocking curve and the preset device design.The influence of the superlattice energy bandgap is investigated by changing the In As and GaSb layer thickness with empirical tight-binding approximation method.It presented that the In As layer thickness is strong related to bandgap,thus the GaSb layer thickness is relatively lower.Based on further semiconductor fabrication technique optimizing,the smooth and no-destructive mesa-isolated is obtained by dry etching and chemical treatment.Si O₂ dielectric layer is synthesized by using inductively coupled plasma chemical vapor deposition system at 75°C.At 300 K,it is clearly appeared lower dark current at reverse bias region and lower resistance in positive region and its performance was better than performed in typical temperature 160°C and 350°C.For high temperature passivation process,the electrical performance is degraded and it may be due to the temperature increases the interface roughness and the element intermixed.Otherwise,the ohmic contact is fulfilled between metal electrode and semiconductor by annealing process.The dark current of unpassivated and passivated device was investigated.For unpassivated samples,a dark current of 2.052×10-4A/cm² and a differential resistance-area of 32.31?.cm² at zero bias voltage are achieved at 77 K.The simulation results of R0 A value for the various sizes of diodes show that surface resistivity is 6.66×103 ?.cm.The detail component of the dark current is analyzed at 77 K.It is also explored that the influence on the dark current by introducing different reduced carrier concentration,and the dark current mechanism would be change from generation-recombination?GR?to tunneling current at 1.2×1016cm-3.And the electron lifetime and the GR lifetime inferred from fitting are 20 ns and 10 ns,respectively.For passivated samples,the dark current and the corresponding differential-resistance value under different bias voltage are studied at temperatures ranging from 77 K to 300 K.The R0 A is 567?.cm² and the dark current is accomplished a magnitude of reduction.According to the dark current fitting results under different temperatures,the diffusion mechanism fitted it well above 150 K,and the GR current is agreed with the temperature ranging from 77K-150 K.Otherwise,the detail component of the dark current at 77 K and 200 K is demonstrated respectively.Otherwise,the dark current mechanisms were investigated at low temperatures?4K-77K?.At the temperatures ranging from 50 K to 77 K,the GR dark current mechanism can fit it well,but when the temperatures is lowered than 50 K,it may be controlled by tunneling or surface leakage current.The detail component of the dark current is investigated at 77 K,20K,and 4K,respectively.At 77 K,The model with GR-only describes accurately the dark current at low applied bias,and then gets smaller,tunneling current is becoming the most part contributing to the total dark current.When the temperature is further decreased to 4K,the tunneling current becomes dominant.The quantum efficiency and spectral response are also presented under different bias voltages and temperatures.It is found that the quantum efficiency?QE?reached the highest point at-20 m V and the measured QE is 16% at 8.64?m with the 50% cutoff wavelength and the specific detectivity attains 1.46×109cm Hz1/2/W,the higher specific detecivity is obtained about 2.25×109 cm Hz1/2/WThe double-heterostructure is prepared and aimed to investigate the contributing mechanism of the surface leakage current between the unpassivated and passivated sample.Then,a model about the passivated mesa surface electron accumulation is proposed,which is good to improve the dark current contribution.