Surface hole gas enabled transparent deep ultraviolet light-emitting diode

Abstract

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.

Comparison of Ultraviolet B Light‐Emitting Diodes with Single or Triple Quantum Wells

“…[3][4][5] Today, the best UVB LEDs exhibit an external quantum efficiency in the range of only a few percent. [6][7][8][9][10][11] Optimization of the semiconductor heterostructure is very important to improve the output power, the operating voltage, and the lifetime of UV LEDs. Therefore, we have previously discussed the influence of the nlayer heterostructure design, [12] the quantum well (QW), and quantum-barrier composition, [13] the QW width [14] as well as the electron blocking layer (EBL) design [15,16] on the emission characteristics and efficiency of triple quantum well (TQW) LEDs in the UVB spectral region.…”

“…[ 3–5 ] Today, the best UVB LEDs exhibit an external quantum efficiency in the range of only a few percent. [ 6–11 ]…”

Improved Efficiency of Ultraviolet B Light‐Emitting Diodes with Optimized p‐Side

“…[ 3–5 ] Today, the best UVB LEDs exhibit external quantum efficiencies of only a few percent. [ 6–11 ]…”

Progress in External Quantum Efficiency for III‐Nitride Based Deep Ultraviolet Light‐Emitting Diodes

“…According to the research results by different groups, however, the external quantum efficiency (EQE) is still lower than 10% for DUV LEDs when the peak emission wavelength is shorter than 280 nm, and most of the reported efficiency droop is higher than 10% for the LEDs at deep ultraviolet range [see Figure (a,b)]. DUV LEDs with low EQE and significant efficiency droop effect cannot efficiently kill all the bacteria in the drinking water with high flow rate . As a result, before the massive penetration into the market to replace the conventional mercury based deep ultraviolet light source, it is essentially important to enhance the EQE for DUV LEDs.…”

“…Summary of the reported (a) EQE and (b) efficiency droop for DUV LEDs by different groups during the last 5 years (2014–2018) …”