Study On The Characteristics Of ZnO/MgZnO Quantum Cascade Detector

In recent years,MgZnO has attracted wide attention as a wide bandgap semiconductor due to its excellent material properties.It is one of the hot toptics in research of optoelectronics and optical communications.Since ZnO and MgZnO can form Two Dimensional Electron Gas?2DEG?with high electron concentration and electron mobility,they have significant potential in the fabrication of heterojunction photovoltaic device.So far,ZnO/MgZnO quantum cascade detector?QCD?has drawn a great deal of interest because of its high detectivity,low dark current and noise,however,the current research is focused on improvements of materials and technique.And the effect of polarization on QCD remains to be study.In addition,noise is one of the most critical parameters for the detector.Thus,the impact of polarization on the performance of ZnO/MgZnO quantum cascade detector and their noise characteristics are studied in our paper.The works are organized as follows:1.According to the theoretical analysis,we are establishing the model of ZnO/Mg_0.3Zn_0.7O quantum cascade detector and studying its basic characteristics.The detector consists of thirty periods of ZnO active absorber quantum wells and"phonon ladder"for electron transport.The electric field,potential distribution,subband energy levels and wave functions are achieved by self-consistent calculation of Schr?dinger-Poisson equations considering the polarization effect.And given some major scattering,including the longitudinal optical phonon scattering?LOS?,piezoelectric scattering?PES?,interface roughness scattering?IRS?,dislocation scattering?DIS?,ionized impurity scattering?IIS?and alloy disorder scattering?ADS?.Base on the model,the effects of different scattering mechanisms on R₀A and detectivity under polarization effect are studied.Then,by simulating the bound-to-bound electronic transport processes under dark,the dark current,R₀A and responsivity of the ZnO/Mg_0.3Zn_0.7O quantum cascade detector are obtained and analyzed.In addition,the detectivities are calculated considering of Johnson noise and photon noise generated by blackbody background radiation.Finally,the influences of the doping concentration in the active quantum wells on the device performance are further studied.The results show that,the dark current with polarization is smaller than that without polarization,and the detection rate is exactly the opposite.The peaks exist around5.55?m and decrease by only 6.37%from 57 K to 400 K without obvious redshift.2.In order to have a better study about the noise properties of quantum cascade detector,the noise equivalent circuit of ZnO/Mg_0.3Zn_0.7O quantum cascade detector is established by calculating the equivalent resistance of each intersubband transition.For sake of clarity,this study only presents a simplified noise equivalent circuit.A theoretical simulation model is established by researching theoretically on the noise of quantum cascade detector,and the contribution of each subband to the noise of the quantum cascade detector,the spectral characteristics and the influence of temperature on the noise characteristics are studied.Because of the doping concentration affects the distribution of electrons which will affect the scattering of the device,the effects of different doping concentrations on the noise properties are investigated.The device structure is optimized to reduce noise by analyzing the noise contribution between the main subband transitions.The results show that when the voltage is less than 0 V,the dark current noise is dominated by the noise generated by the electronic transition between the E1'-E2 and E1'-E3 transitions.When the voltage is greater than 0 V,the dark current noise is dominated by the contributions of the E2-E1 and E5-E1 transitions.For the spectral characteristics,the cutoff frequency is 2.7GHz,and the noise signal is nearly-261 dBm/H.The noise dark current density increases with increasing temperature,but the rate of increase decreases.In addition,as the doping concentration increases,the dark current noise density rises,but the noise equivalent power decreases.The dark current noise density is reduced by optimizing the structure of device.Therefore,the work in this chapter is very meaningful for designing high quality QCDs.The work of the paper could provide some theoretical references for the design and optimization ZnO/MgZnO quantum cascade detectors.