The inherent deep-level nature of acceptors in wide-band-gap semiconductors makes p-ohmic contact formation and hole supply difficult, impeding progress for short-wavelength optoelectronics and high-power high-temperature bipolar electronics. We provide a general solution by demonstrating an ultrathin rather than a bulk wide-band-gap semiconductor to be a successful hole supplier and ohmic contact layer. Free holes in this ultrathin semiconductor are assisted to activate from deep acceptors and swept to surface to form hole gases by a large electric field, which can be provided by engineered spontaneous and piezoelectric polarizations. Experimentally, a 6 nm thick AlN layer with surface hole gas had formed p-ohmic contact to metals and provided sufficient hole injection to a 280 nm light-emitting diode, demonstrating a record electrical-optical conversion efficiency exceeding 8.5% at 20 mA (55 A cm −2 ). Our approach of forming p-type wide-band-gap semiconductor ohmic contact is critical to realizing high-efficiency ultraviolet optoelectronic devices.

No abstract

We report a high-power ultraviolet C-band light-emitting diode (UVC LED) with peak wavelength at 268 nm delivering 199 mW optical power at 350 mA direct current. The peak wall-plug and external quantum efficiencies are greater than 10% and 13%, respectively. We developed an approach to determine light-extraction efficiency (LEE) and internal quantum efficiency (IQE) based on the carrier recombination rate equation and used it to analyze the junction-temperature-dependent optical power behavior. For this LED, we obtained a LEE of ~16% and a peak IQE of ~83%. The efficiency droop percentage was quantified to be ~20% at 350 mA, owing to Auger and other higher order carrier losses.

After assigning a thickness d to the carrier recombination region of a light emitting diode (LED), we show that the ABC model involving Shockley–Read–Hall non-radiative, radiative, and Auger recombination coefficients, i.e., A, B, and C, respectively, can bring new insight into the radiative recombination process. In order to fit external quantum efficiency (EQE) data of ultraviolet C-band (UVC) as well as blue LEDs, the ABC model requires the product [Formula: see text] to be invariant of the injection current. This can be understood that as the thickness of the recombination region increases the radiative recombination coefficient decreases due to reduced electron–hole wavefunction overlaps. For an LED with high internal quantum efficiency (IQE), its quality factor Q ([Formula: see text]) usually undergoes a noticeable drop as the injection current increases to pass the current of maximal EQE. This is due to an increase in the thickness of the recombination region and, hence, a reduction in the radiative recombination coefficient as the injected carriers start to drift or diffuse to involve more quantum wells for light emission. Applying this ABC model, we analyze a high-efficiency 268 nm UVC LED, which delivers ∼199 mW optical power under a direct current of 350 mA and obtains a maximal IQE of ∼86.4% and an effective light extraction efficiency of ∼15.3%.

Unable to control at long range is the shortage of DALI protocol. In order to solve this problem, a remote control scheme based on GPRS module is designed. In the hardware part, the GPRS module is set as a communication device of main controller, and the interface of MCU supports to the DALI protocol. In the software part, the control mechanism between the main controller and mobile terminal is realized. The software runs on the mobile terminal is developed, which is based on J2ME. The experimental result shows that the system responses are fast when user is at long range. It is of significant meaning for this design scheme on the development of advanced indoor lighting automation system.