Quasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN template

The high power GaN-based blue light emitting diode （LED） on an 80%tm-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition （MOCVD）, hydride vapor-phase epi- taxial （HVPE）, and laser lift-off （LLO）. Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction （XRD）, high resolution transmission electron microscope （HRTEM）, Rutherford back-scattering （RBS）, photoluminescence, current-voltage and light output-current measurements. The width of （0002） reflection in XRD rocking curve, which reaches 173＂ for the thick GaN template LED, is less than that for the conventional one, which reaches 258＂. The HRTEM images show that the multiple quantum wells （MQWs） in 80%tm- thick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-~m-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80%tin-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.     

Gradual variation method for thick GaN heteroepitaxy by hydride vapour phase epitaxy

Two strain-state samples of GaN, labelled the strain-relief sample and the quality-improved sample, were grown by hydride vapour phase epitaxy (HVPE), and then characterized by high-resolution X-ray diffraction, photoluminescence and optical microscopy. Two strain states of GaN in HVPE, like 3D and 2D growth modes in metal-organic chemical vapour deposition (MOCVD), provide an effective way to solve the heteroepitaxial problems of both strain relief and quality improvement. The gradual variation method (GVM), developed based on the two strain states, is characterized by growth parameters' gradual variation alternating between the strain-relief growth conditions and the quality-improved growth conditions. In GVM, the introduction of the strain-relief amplitude, which is defined by the range from the quality-improved growth conditions to the strain-relief growth conditions, makes the strain-relief control concise and effective. The 300-μm thick bright and crack-free GaN film grown on a two-inch sapphire proves the effectiveness of GVM.     

GaN基微米LED大注入条件下发光特性研究

利用变注入强度的电致发光(EL)测试和数值模拟方法研究了微米LED大注入条件下的发光特性。EL测试结果显示,微米LED(10μm)在工作电流密度高达16kA/cm2时光功率密度输出未饱和,同时不存在明显的由于自热效应引起的发光波长红移。和300μm LED相比,相同注入水平下,10μm LED的EL峰值波长相对蓝移,表明微米LED中存在应力弛豫,10μmLED相对300μm LED应力弛豫大了约23%。APYSY模拟发现,由于应力弛豫和良好的电流扩展,微米LED中电流分布和载流子浓度更加均匀,这种均匀的分布使得微米LED具有高的发光效率,同时能够承受高的电流密度。     

Quasi-homoepitaxial GaN-based blue light emitting diode on thick GaN template

The high power GaN-based blue light emitting diode (LED) on an 80-μ-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition (MOCVD), hydride vapor-phase epitaxial (HVPE), and laser lift-off (LLO). Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), Rutherford back-scattering (RBS), photoluminescence, current-voltage and light output-current measurements. The width of (0002) reflection in XRD rocking curve, which reaches 173" for the thick GaN template LED, is less than that for the conventional one, which reaches 258". The HRTEM images show that the multiple quantum wells (MQWs) in 80-μm-thick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-μm-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80-μm-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.