Study On Material Characteristics And Dislocations Of GaN On Off-axis Si Substrates

Recently,a number of major technoligical breakthroughs have been made in the crystal growth and device fabrication of GaN based LED,and it has been widely used in areas such as traffic display,large screen dispiay and so on.But for actually entering the huge marketing of indoor lighting actually,there are also much effort have to be done on improving power efficiency and reducing costs.Compared to sappire and SiC,Si substrate has some advantages for GaN hetero-epitaxial,such as cheapness,mature technology,and it can be done and be removed easily for preparing vertical LED devices.The shortcomings of Si substrate is also obvious,there is a huge lattice mismatch and thermal mismatch between GaN and Si,this makes a large number of misfit dislocations in the epitaxial GaN materials which can affecting the opitcal and electrical properties of LED devices.In recent years,Si substrate GaN-based LED has been push in dustrialization successfully in our laboratory,and it also breaks the original pattern of LED market,but there are also a lot of work to do in epitaxial growth and device fabrication.This research word is mainly divided into two parts:First,on the basis of the accurate measurement of Si substrate cut-off angle,the effect of the cut-off angle for the Si substrate GaN-based LED epitaxial films is studied;Second,the dislocations of GaN epitaxial films on different Si substrate is studied.At the end,we obtain the following results:1.The cut-off angle of three kinds of Si substrates are measured accuratly in the X-ray diffraction method,the three Si substrates are Si(111),Si(111)+1°and Si(111)+2°.The result confirm the cut-off angle of these kinds of Si substrates do not affect the next research work,while also use this method in LED field successfully.2.The epitaxial films of GaN based LED on these three Si substrates are tested by XRD,AFM and fluorescence microscopy in four part:the crystal quality, the stress and strain,surface morphology, the informationaspects of the quantum wells.The results show thatrthe epitaxial films on the Si(111)+1°substrate are as well as or better than the epitaxial films on the Si(111) substrate in the crystal quality.stress-strain and small-scale surface roughness.while the wide range surface roughness is poor, and the Si(111)+2°is poorer. So we think that if a cut-off degee is in less than l°to obtain the value of the appropriate size it will be conductive to epitaxial films growth.3.The dislocation of epitaxial films on three kinds of Si substrate is studied by XRD,the three substrates are Si(111) high-resistance,Si(110) high-resistance and Si(110) low-resistance.According to the XRD calculation,the dislocation density of three samples are1.5715×109,1.0399×109and2.0257×109/cm2.The dislocation density of the epitaxial films on the Si(110) high-resistance substrate show that the scrow dislocation density is greater than the edge dislocation density,which we think is related with high density of impurity.4.The dislocation of the three samples were studied by the way of H3PO4etching,firstly the best corrosion time and temperature of each sample was explored.then observed the size and shape characteristics of the pits though AFM.