Graphene transparent conductive electrode (TCE) applications in nitride light emitting diodes (LEDs) are still limited by the large contact resistance and interface barrier between graphene and p-GaN. We propose a hybrid tunnel junction (TJ)–graphene TCE approach for nitride lateral LEDs theoretically and experimentally. Through simulation using commercial advanced physical models of semiconductor devices (APSYS), we found that low tunnel resistance can be achieved in the n+-GaN/u-InGaN/p+-GaN TJ, which has a lower tunneling barrier and an enhanced electric field due to the polarization effect. Graphene TCEs and hybrid graphene–TJ TCEs are then modeled. The designed hybrid TJ–graphene TCEs show sufficient current diffusion length (Ls), low introduced series resistance, and high transmittance. The assembled TJ LED with the triple-layer graphene (TLG) TCEs show comparable optoelectrical performance (3.99 V@20 mA, LOP = 10.8 mW) with the reference LED with ITO TCEs (3.36 V@20 mA, LOP = 12.6 mW). The experimental results further prove that the TJ–graphene structure can be successfully incorporated as TCEs for lateral nitride LEDs.Keywords: current spreading; gallium nitride; graphene; light emitting diodes; transparent conductive electrodes; tunnel junction

The electrical characteristics of metallization contacts to flat (F-sample, without wet-etching roughed) and wet-etching roughed (R-sample) N-polar (Nitrogen–polar) n-GaN have been investigated. R-sample shows higher contact resistance (Rc) to Al/Ti/Au (∼2.5 × 10–5 Ω·cm2) and higher Schottky barriers height (SBH, ∼0.386 eV) to Ni/Au, compared with that of F-sample (∼1.3 × 10–6 Ω·cm2, ∼0.154 eV). Reasons accounting for this discrepancy has been detail investigated and discussed: for R-sample, wet-etching process caused surface state and spontaneous polarization variation will degraded its electrical characteristics. Metal on R-sample shows smoother morphology, however, the effect of metal deposition state on electrical characteristics is negligible. Metallization contact area for both samples has also been further considered. Electrical characteristics of metallization contact to both samples show degradation upon annealing. The VLED chip (1 mm × 1 mm), which was fabricated on the basis of a hybrid scheme, coupling the advantage of F- and R-sample, shows the lowest forward voltage (2.75 V@350 mA) and the highest light output power.Keywords: electrical characteristics; GaN; metallization contacts; N -polar; vertical light emitting diodes;

A thermal stress aided electroless etching (TSEE) process of epitaxial GaN on sapphire has been demonstrated experimentally and theoretically. The sapphire has been successfully separated from the epitaxial GaN by electroless etching assisted by the thermal peeling stress at the GaN/sapphire interface. ANSYS simulation indicates a sharp increase in peeling stress at the edge of the chip. The mechanism of the TSEE process has been elucidated in macro- and micro-interpretation in this paper, which is based on a charge transfer reaction model with a thermodynamic cycle and an Arrhenius equation. The influences of etching temperature (ET) and etchant concentration (EC) on the TSEE process were quantitatively analyzed based on experimental results. X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) results show an improvement in the epitaxial GaN crystallinity with the TSEE process. Analysis of the mechanisms of the TSEE process will undoubtedly deepen our understanding of semiconductor etching and facilitate more potential applications.