Investigation Of Novel Semiconductor Heterostructures Characteristics For Optical Detection

As a new kind of heterostructure semiconductor,ZnMgO/ZnO has attracted much attention for great potential in the field of photoelectrical devices.In recent years,although two-dimensional electron gas?2DEG?transport properties of ZnMgO/ZnO heterostructures have made much progress,a further exploration of high-field transport characteristics and scattering mechanisms limiting 2DEG mobility at low temperature,for example,alloy cluster scattering?ACS?is still required.In addition,a thin MgO layer is inserted on the ZnMgO/ZnO heterojunction interface to form ZnMgO/MgO/ZnO heterostructures.ZnMgO/MgO/ZnO heterostructures have tremendous development potential for fabrication in high-frequency and high-power devices due to its larger 2DEG concentration and mobility than ZnMgO/ZnO quantum well?QW?.But the theoretical studies of ZnMgO/MgO/ZnO heterostructures mainly focus on mobility characteristics analysis,the impact of built-in electric field?BEF?induced by polarization effect on intersubband transition optical absorptions?ITOA?properties in ZnMgO/MgO/ZnO heterostructures has never been reported.In view of the above questions,the effect of ACS on 2DEG transport characteristics of ZnMgO/ZnO heterostructures and ZnMgO/MgO/ZnO QW material properties have been studied.The details are as follows:1.The self-consistent numerical solution of the Schr?dinger and Poisson equations is performed to acquire the subband energy levels,the corresponding wave functions and2DEG concentration.For low temperature,some major scattering mechanisms of ZnMgO/ZnO heterostructures are considered,including ACS,dislocation scattering?DIS?,interface roughness scattering?IRS?,phonon scattering?PHS?,and alloy disorder scattering?ADS?.Then,the total 2DEG mobility is calculated by using Matthiessen's rule.In this work,the influence of ACS on low-temperature electron mobility is mainly investigated.Meanwhile,based on the electronic band structures of ZnO and ZnMgO and correlated parameters obtained by first-principles calculations and considering ACS,DIS,IRS,ADS,and PHS,Monte Carlo?MC?models for simulating heterostructures electron transport are built including three-valley and five-valley MC models.Further,the effect of ACS on the low-field and high-field electron transport properties of ZnMgO/ZnO heterostructures is simulated.The results show that ACS is caused by alloy compositional fluctuations and will induce energy levels fluctuations in the channel,so the composition fluctuations of the Zn_1-xMg_xO barrier will affect 2DEG mobility.The 2DEG mobility limited by ACS decreases with the increase of Mg composition fluctuation.Besides,ACS is one of the dominant scattering mechanisms at low temperature.2.The eigenstates and eigen-energies of 2DEG in wurtzite Zn_1-xMg_xO/MgO/ZnO QW with an inserted MgO layer are obtained from the self-consistent solution of the Schr?dinger and Poisson equations.Meanwhile,the influence of the built-in electric field induced by spontaneous polarization?SP?and piezoelectric polarization?PE?is taken into consideration.Then,size effect?SE?and ternary mixed crystal effect?TMCE?of 2DEG distribution in Zn_1-xMg_xO/MgO/ZnO heterostructures is studied.Further,the density matrix formalism is adopted to calculate the intersubband optical absorptions and the impact of the structure parameters on optical absorption of intersubband transition in Zn_1-xMg_xO/MgO/ZnO QW.The results show that the increase of the thickness of inserted MgO layer and the Mg composition of Zn_1-xMg_xO barrier will enhance the built-in electric field in the ZnO layer,making 2DEG closer to the interface of MgO/ZnO heterostructure.Moreover,Mg composition of the ternary mixed crystal barrier,well width,and thickness of barrier will affect optical absorption coefficient.The absorption peak for ITOA is increased in energy when Mg composition is increased,and it is increased in magnitude with the increasing Mg composition.Furthermore,the absorption peak for ITOA is decreased in energy with the increase of well width,and it is decreased in magnitude when well width is increased.The absorption peak for ITOA is decreased in energy with the increasing thickness of barrier,and it is decreased in magnitude when thickness of barrier is increased.The research can provide some theoretical references for designing and fabricating ZnMgO/ZnO and ZnMgO/MgO/ZnO heterostructure devices with high performance.