Electro-ridge for large injection current of micro-size InGaN light emitting diode

Abstract

High-performance, blue micro-size InGaN light emitting diodes (LEDs) with diameters of 3 to 20 μm have been fabricated. An ion implantation technique and a 12 micron electro-ridge were used to simplify fabrication processes. The 3 to 20μm LEDs that exhibited a large emission photon blue shift (87.5meV ~52.9meV) were observed in electro-luminescence (EL) spectra. Under an increased injection current, the quantum wells become populated with charge carriers, which screened the internal piezoelectric field and caused the energy blue shift of EL eventually. A high injection current caused a high junction temperature that narrowed the band gap (red shift). The size dependent energy shift is largely owing to the competition between the blue and the red shifts. At a bias voltage of 8.96V (which is 140% of the turn on voltage, 6.4V), the 10 μm device exhibited an injection current of 7.9mA. This value exceeds that in literature, i.e., 4mA at a bias voltage of 14V (which is 140% of the turn on voltage, 10V). This phenomenon may be owing to that the ion implantation and electro-ridge designs herein involved a lower series resistance. The external quantum efficiencies (E.Q.E.) of the micro size LEDs herein were all 0.4%~3.3%, which is better than the values reported in literature, which were ranged between 0.004% and 1.29% for an individual LED and an array LED, respectively. The E.Q.E. of the 15μm device at maximum injection current had the optimum value yet obtained for micro-size LEDs. The dependence of the blue shift and the E.Q.E. on the size warrants further study.