Study On The MOCVD Growth And Infrared Characteristics Of GaSb/InSb/InP Infrared Detector Structures

In the field of Infrared Communications,Gas Monitoring,Remote Sensing Technique and so on,there is an urgent need for semiconductor infrared detectors in the wave band of 3-5?m.Uncooled infrared detectors facilitate the integration of devices and lighter detection systems,according to that there is no refrigeration equipment.They have many advantages such as low power consumption,low cost,and wide response spectrum,which satisfy the development of third-generation infrared detectors.As a typical narrow bandgap semiconductor material,InSb is an ideal material for infrared detectors,owe to the advantages of high quantum efficiency,fast response,stability.However,the output noise at room tempereature caused by the recombination mechanisms in the InSb is high,which makes it difficult for InSb to be applied in the manufacturing of non-infrared detectors.In order to solve the problem of high output noise of InSb infrared detectors at room temperature,a heterojunction PIN structure of GaSb/InSb/InP is proposed here,in which GaSb and InP with wider bandgap are P-layer and N-layer respectively.In this structure,P-GaSb and N-InP are used as hole-transport layer and electron-transport layer,respectively;unintentionally doped InSb,used as I-layer,is responsible for absorbing the input infrared radiation and emitting non-equilibrium carriers,thereby forming a photocurrent.There are two distinct advantages of the PIN hetero-junction structure over the InSb homogeneous PIN structure:First,the recombination rates of the recombination mechanisms in GaSb and InP is low,owing to the large band gaps.So the effective area of the recombination mechanisms can be effectively limited to the inside of the I-layer,which increats the non-equilibrium carrier life time in P-layer and N-layers.Then the noise current inside the detector caused by the recombination mechanisms will decrease,so the external quantum efficiency of the device will increase at the same time.Besides,the GaSb and InP materials will introduce two gaps of 0.52 eV and 0.98eV in the conduction band and valence band,respectively,when heterojunctions are formed in contact with InSb.Therefor,an effective barrier of electron and a barrier of hole are forming,which will restrict the diffusion of carriers in the InSb of I-layer,so that the noise current caused by the diffusion can be suppressed.In addition,the I-layer is fully depleted under reverse bias,and the concentration of free carriers in the I-layer is extremely low under the effect of minority carries extraction,which reduces the recombination rate of the Auger recombination mechanism.So the dark current produced by the Auger recombination effect can be reduced to a certain extent.The research of GaSb/InSb/InP infrared detector structure is mainly divided into two parts,modeling simulation and experimental growth.The Silvaco TCAD simulation tool is used during the modeling and simulation process of the device.The simulation started from the carrier continuity equation combined with the drift-diffusion model and the parabolic approximation of the energy band.Then the simplified energy band and carrier distribution of the device were obtained.At the same time,the infrared absorption characteristics and dark current mechanism of the device structure were investigated,showing that the cutoff wavelength was 6.8?m.And the main factor of the device dark current at room temperature was proved to be the Shockley-Raid recombination mechanism.As for the experimental growth,Metal-Organic Chemical Vapor Deposition?MOCVD?technology was used as the growth process,and the growth parameters including growth temperature,pressure,and gas phase?/?ratio were investigated by the comparative experiment,during the growth of InSb and InP epitaxial layers.The influence of the parameters on the surface morphology and crystallization quality of the epitaxial layer was analyzed to determine the optimum growth conditions.An InSb-layer and a GaSb-layer were grown sequentially on an InP substrate to prepare the basic device structure,according to the optimum process parameters.Then electrodes were prepared by evaporation technique,and the I-V characteristics of the devises under reverse bias were tested using a semiconductor analyzer.The test results showed that,the main limitation of the device performance was the Shockley-Raid recombination process,the dark current of the device was 0.26 A·cm^-2,and the quality factor R₀A was0.1?·cm².