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We demonstrate a GaN-based flip-chip LED (FC-LED) with a highly reflective indium-tin oxide (ITO)/distributed Bragg reflector (DBR) ohmic contact. A transparent ITO current spreading layer combined with TaO/SiO double DBR stacks is used as a reflective p-type ohmic contact in the FC-LED. We develop a strip-shaped SiO current blocking layer, which is well aligned with a p-electrode, to prevent the current from crowding around the p-electrode. Our combined numerical simulation and experimental results revealed that the FC-LED with ITO/DBR has advantages of better current spreading and superior heat dissipation performance compared to top-emitting LEDs (TE-LEDs). As a result, the light output power (LOP) of the FC-LED with ITO/DBR was 7.6% higher than that of the TE-LED at 150 mA, and the light output saturation current was shifted from 130.9  A/cm for the TE-LED to 273.8  A/cm for the FC-LED with ITO/DBR. Owing to the high reflectance of the ITO/DBR ohmic contact, the LOP of the FC-LED with ITO/DBR was 13.0% higher than that of a conventional FC-LED with Ni/Ag at 150 mA. However, because of the better heat dissipation of the Ni/Ag ohmic contact, the conventional FC-LED with Ni/Ag exhibited higher light output saturation current compared to the FC-LED with ITO/DBR.

High-efficiency GaN-based visible flip-chip miniaturized-light emitting diodes (FC mini-LEDs) are desirable for developing white LED-backlit liquid crystal displays. Here, we propose a full-angle Ti3O5/SiO2 distributed Bragg reflector (DBR) for blue and green FC mini-LEDs to enhance the device performance. The proposed full-angle Ti3O5/SiO2 DBR is composed of different single-DBR stacks optimized for central wavelength in blue, green, and red light wavelength regions, resulting in wider reflective bandwidth and less angular dependence. Furthermore, we demonstrate two types of GaN-based FC mini-LEDs with indium-tin oxide (ITO)/DBR and Ag/TiW p-type ohmic contacts. Experimental results exhibit that the reflectivity of full-angle DBR is higher than that of Ag/TiW in the light wavelength range of 420 to 580 nm as the incident angle of light increases from 0° to 60°. As a result, the light output powers (LOPs) of blue and green FC mini-LEDs with ITO/DBR are enhanced by 7.7% and 7.3% in comparison to blue and green FC mini-LEDs with Ag/TiW under an injection current of 10 mA. In addition, compared with FC mini-LED with Ag/TiW, light intensity of FC mini-LED with ITO/DBR is improved in side direction, which is beneficial to mix light in backlight system of liquid crystal displays (LCDs).

In this work, one type of direct current high voltage light‐emitting diode (DC‐HV LED) and six types of alternating current high voltage LEDs (AC‐HV LEDs) are demonstrated. Comparative current‐voltage (I–V) and light output power (LOP)‐current (L‐I) characteristics are performed between 24 V DC‐HV LED and 24 V AC‐HV LEDs with eight working cells. The AC‐HV LED has relatively larger wall‐plug efficiency (WPE) than DC‐HV LED over a current density range from 0 to 152 A cm−2. The effect of the layouts on the optical and electrical properties of AC‐HV LEDs is further investigated. Owing to larger heat dissipation area and fewer number of chips, our combined numerical and experimental results demonstrate that the AC‐HV LED I has a more favorable current spreading uniformity compared to other AC‐HV LEDs. In addition, it is found that the LOP of AC‐HV LEDs is dependent on both the number of working cells and the ratio of radiation area to total chip area. Larger ratio of light emission area to total chip area can be obtained by decreasing the area of rectifier cells. Therefore, in order to achieve a much higher LOP, AC‐HV LEDs have to be designed with smaller area of rectifier cells and with more working cells simultaneously.