Study On Microdefects And Device Properties In Epitaxial Growth Of Compound Semiconductors

Compound semiconductors have superior optoelectronic properties,high speed,high frequency,high power,high temperature resistance and high radiation,and are widely used in optoelectronic devices and power devices.This paper focuses on the defects of silicon carbide and gennanide materials in compound semiconductors and their effects on device performance.On the one hand,the surface defects and deep level defects in 4H-SiC epitaxial wafers prepared by CVD were studied.The effects of related defects on device performance were clarified from the aspects of physical morphology,structural characterization and electrical properties,and the high quality 4H-SiC Schottky diode(SBD)was realized by optimizing the process parameters of CVD.On the other hand,the physical mechanism of dark current and noise of the telluride type ? superlattice infrared detector,the deep level defects in the superlattice material and the relationship between them are deeply studied.The specific research contents are as follows:1)The influence of key process parameters of CVD on surface defects of 4H-SiC epilayer was studied.Three sets of 4-inch 4H-SiC epitaxial wafers with different CVD process parameters(carbon to silicon ratio,doping concentration and growth rate)were designed and prepared.Scanning electron microscopy(SEM),atomic force microscopy(AFM),photoluminescence(Micro-PL),Raman(Micro-Raman)and transmission electron microscopy(TEM)were used to analyze the microstructure and formation mechanism ol surface defects.The epitaxial defect density was successfully reduced by process optimization,and the influence of surface defects on the electrical properties of 4H-SiC SBD was analyzed.2)The effects of different C/Si ratios(C/Si=0.9,1 and 1.1)on the performance of Ni/4H-SiC SBD were investigated.It is found that the reverse leakage current and 1/f noise of Ni/4H-SiC SBD increase with the increase of C/Si ratio.The DLTS results show that the 21/2 defect concentration hardly changes with the growth parameters.Further experimental results show that the main reason for the influence of different C/Si ratios on the performance of Ni/4H-SiC SBD is due to the different degree of interface state density caused by the crystal quality,which leads to the change of reverse leakage current and noise of the device.3)The effect of Ti deep level defects on the electrical properties of Ni/4H-SiC SBD was investigated.A double barrier occurs in the forward I-V characteristic,and the contribution of the current flowing through the high and low barrier regions is explained by introducing the proposed analysis model in the inverse I-V characteristic analysis.Fitting calculation analysis shows that the contribution of current in the low barrier region plays a major role.The DLTS characterization further revealed that there were two electron defects(Ec-0.16 eV and Ec-0.67 eV)in the sample.The former is an intrinsic defect that may be related to carbon vacancies.The latter is a Ti impurity defect.Ti impurity defects are the cause of the decrease of barrier height and seriously affect the electrical properties of Ni/4H-S C SBD.4)The dark current dominated by the G-R current observed in the 2.5 lum InGaAs/GaAsSb superlattice detector grown by the MBE method is due to the presence of deep level defects.The DLTS results indicate that there are three electron defects El(Ec-0.11 eV),E2(Ec-0.28 eV),E3(Ec-0.17 eV)and a hole defect HI(Ev+0.25 eV)in the temperature range of 77?300 K,respectively.The each defect parameter and the concentration distribution of defects were analyzed in depth.In addition,the defects El and H1 obtained by the relationship between the DLTS peak and the fill pulse width tp are attributed to the localized states of extended defects,and E2 is attributed to the bandlike states of extended defects.5)The crystal quality and photoelectric properties of the 10 ?m InAs/GaSb T2SL detector were studied.The Raman analysis showed that the superlattice crystal was good and no relevant interface modes were observed.The noise test was used to deeply analyze the 1/f noise of the detector mainly due to the side leakage caused by the surface state of the superlattice material.In addition,under different reverse bias voltages,excitation wavelengths and temperature conditions,the effects of voltage and temperature on the responsiveness(Ri),noise equivalent power(NEP)and detection rate(D*)were studied by scanning photocurrent response test system.