Single p n homojunction white light emitting diodes based on high performance yellow luminescence of large scale GaN microcubes
Cubic phase (zinc blende) GaN (referred to as c GaN) based phosphor free white light emitting diodes (LEDs) can exhibit superior characteristics and ultrahigh efficiency compared with conventional hexagonal phase (wurtzite) GaN (referred as h GaN) based examples. However, one notorious issue is low quality of c GaN due to thermodynamical instability of cubic phase, epilayer substrate chemical incompatibility, and large lattice mismatch during epitaxial deposition, giving rise to insufficient light emission efficiency. Therefore, improving the quality of c GaN is a key step towards high performance white LEDs. Here, we report the growth of high quality single crystalline GaN microcubes (MCs) with pure zinc blende phase for large scale production by the chemical vapor deposition method. From the GaN MCs, high performance yellow luminescence (YL) is observed by different temperature photoluminescence spectra and the possible origin of the YL band is investigated. Furthermore, the fabricated phosphor free single homojunction based on individual GaN MCs showed a diode nonlinear rectification behavior and the electroluminescence exhibited white emission when the operating voltage is 12 V. At room temperature, due to the reduction of threading dislocation density and the absence of piezoelectric polarization of the zinc blend phase GaN, the device can exhibit an internal quantum efficiency of ~99.2% and virtually no efficiency droop as the injection current increases. The device also exhibits an output power of ~4.4 mW at a typical operating current of 20 mA, which is approximately 50% stronger than that of conventional h GaN homojunction LEDs.