Wet etching has been widely used in defect evaluation for Ga-face GaN and surface roughness for N-face GaN dodecagonal pyramids has been fabricated on laser-lift-off N-face GaN by hot phosphor acid etching.The dodecagonal pyramid shows twelve facets including six{20-2-3}and six{22-4-5}planes.From cross-sectional TEM image,it is shown that the pyramid corresponds to the top of the edge dislocation.Compared with hexagonal pyramid-surface light emitting diodes(LEDs)etched by commonly used photoelectrochemical(PEC)process in KOH aqueous,the dodecagonal pyramid-surface LEDs show improved light extraction efficiency because of more facets,which effectively reduces the total internal reflection.
QI ShengLi,CHEN ZhiZhong,SUN YongJian,FANG Hao,TAO YueBin,SANG LiWen,TIAN PengFei,DENG JunJing,ZHAO LuBing,YU TongJun,QIN ZhiXin&ZHANG GuoYi State Key Laboratory for Artificial Microstructure and Mesoscopic Physics,School of Physics,Peking University,Beijing 100871,China
Au/Sn solder bonding on Si substrates was used to fabricate the GaN-based vertical structure light emitting diodes (VSLEDs). The phase reaction of Au/Sn solder under different bonding conditions was investigated by the measurement of electron back scattering diffraction (EBSD), and the characteristics of VSLED were analyzed by scanning acoustic microscope (SAM), Raman scattering, current-voltage (I-V) and light output-current (L-I) curves. After the bonding process, horizontal stripes of Au/Sn phase (δ phase) and Au5Sn phase (ζ phase) were redirected to vertical stripes, and δ phase tended to move to the solder joint. Sn interstitial diffusion led to the distribution of δ phase and voids in Au/Sn solder, which could be seen in SAM and SEM images. Vertical distribution of the δ phase and ζ phase with proper voids in the Au/Sn bonding layer showed the best bonding quality. Good bonding quality led to little shift of the E2-high mode of Raman spectra peak in GaN after laser lift off (LLO). It also caused more light extraction and forward bias reduction to 2.9 V at 20 mA.
TIAN PengFei, SUN YongJian, CHEN ZhiZhong, QI ShengLi, DENG JunJing, YU TongJun, QIN ZhiXin & ZHANG GuoYi State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
