Growth And Optical Properties Of GaN Based Micro-Pyramid

Commercial two-dimensional GaN based thin film LED structure has many problems such as high dislocation densities,efficiency droop,quantum-confined Stark effect and green gap,which will influence its application in high power,high brightness and long life of full-color LEDs.Therefore,it is of great significance to study the growth and optical properties of novel GaN micro/nano structures.In this study,the GaN micro-pyramid was successfully fabricated after SiN_x was deposited in situ on an undoped GaN layer by metal-organic chemical vapor deposition(MOCVD),and the effects of the growth conditions such as temperature,growth time,V/III ratio and pressure on its morphology were studied in detail.Then,three periods of InGaN/GaN multiple quantum wells(MQWs)were grown on the semi-polar facet of the GaN micro-pyramid,of which the luminescence properties and luminescence mechanism were studied in detail.The specific results are shown as follows:(1)The migration rate of atoms is greatly affected by the temperature,which has a great influence on the morphology of the GaN micro-pyramid.When the temperature was 1075°C,the GaN micro-pyramid with six semi-polar{10-11}facets and a small polar(0001)facet were fabricated.The size and density of the GaN micro-pyramid can be affected by the growth time,while the size increases and the density decreases with the extension of time.The growth rate of the semi-polar facet and its morphology can be affected by V/III ratio and pressure,and the GaN micro-pyramid under high pressure and low V/III ratio has a larger size and a large(0001)surface,while that under low pressure and high V/III ratio has the smaller size and a smal(0001)surface.The semi-polar facet of the GaN micro-pyramid is N surface(2)The three-period of InGaN/GaN MQWs were grown on the semi-polar facet of the GaN micro-pyramid by MOCVD.The top(0001)surface of the GaN micro-pyramid disappeared after the deposition of MQWs.The wavelengths of the cathodoluminescence spectra at different positions on the semi-polar facet of the InGaN/GaN micro-pyramid are different,indicating the different distribution of In element.The InGaN/GaN MQWs was characterized by transmission electron microscopy,and the migration mechanism of In atoms on the InGaN/GaN micro-pyramid was explained by the results of the cathodoluminescence spectra.The polarization field of the semi-polar facet of InGaN/GaN micro-pyramid is weaker after the deposition of MQWs.This structure can be applied in full color LED.