Molecular beam epitaxy growth of AlGaN quantum wells on 6H-SiC substrates with high internal quantum efficiency

Abstract

The authors report the development of high internal quantum efficiency AlN/AlGaN/AlN double heterostructures and AlGaN/AlN multiple quantum wells (MQWs) grown on 6H-SiC and 4H-SiC substrates of various miscuts by plasma-assisted molecular-beam epitaxy. The authors find that the luminescence spectra for identical MQWs show a single peak across the gap, with a wavelength that is redshifted by $20 nm as the excess Ga during growth of the wells increases. The internal quantum efficiency of the double heterostructures emitting at 250 nm is found to be 43%, and that of the multiple quantum wells emitting at 245 nm is 68%. These results suggest that AlGaN alloys on SiC substrates are capable of producing deep-ultraviolet emitters with high efficiency. The authors propose that these results can be accounted for by the introduction of lateral band structure potential fluctuations due to the changing of the growth mode from physical vapor phase epitaxy to liquid phase epitaxy (LPE) as the excess gallium increases. In this LPE mode the arriving active nitrogen species from the plasma source and aluminum atoms from the aluminum effusion cells dissolve in the excess liquid gallium and incorporate into the film from the liquid phase.

Ultraviolet optoelectronic devices based on AIGaN alloys grown by molecular beam epitaxy

“…[108] Zhang et al reported that such AlGaN/ AlN MQWs emitting at 245 nm have an IQE of 68%. [107] These values of IQE for AlGaN MQWs emitting at 250 nm are comparable with those of InGaN MQWs. [106] In the case of InGaN QWs, the high IQE is generally attributed to band-structure potential fluctuations due to compositional inhomogeneities in these alloys.…”

“…[107] Growth of AlGaN alloys and QWs on SiC for emitters has several advantages. The lattice mismatch between SiC and AlN is only ∼1%.…”

AlGaN/AlN quantum dots for UV light emitters

“…In the recent years, AlGaN-based UV lightemitting diodes (LEDs) [1,2] have appeared as promising candidates to replace mercury lamps due to their advantages of compactness, portability, long lifetime and environmental friendliness. Although AlGaN/AlN quantum wells (QWs) with high internal quantum efficiency (IQE) have been reported [3][4][5], the fabrication of electrically-driven UV LEDs must face the challenges of p-type doping and contacting high-Al-content AlGaN layers, which result in extremely low external quantum efficiency [6] (EQE < 1% for UV LEDs emitting below 250 nm). Electron-pumped UV (EPUV) sources incorporating a miniaturized electron source [7] have been introduced as an alternative approach to circumvent the p-doping issue.…”

Growth and characterization of Cr-doped semi-insulating GaN templates prepared by radio-frequency plasma-assisted molecular beam epitaxy

“…The symmetric (0002) and asymmetric (101 2) full width have fitted widths of 394 and 778 arc sec which is less than that of the Cr-doped GaN. The dislocation density in this film was determined by measuring the x-ray rocking curves of (0002) and (101 2) diffraction spots and fitting the data to the formula [26][27][28]:…”