UVA and UVB light emitting diodes with Al _y Ga_1−y N quantum dot active regions covering the 305–335 nm range

Abstract

Ultra-violet (UV) light emitting diodes (LEDs) using III-N quantum dot (QD) active regions have been fabricated by molecular beam epitaxy on (0001)-oriented sapphire substrates. By using the epitaxial compressive stress between the QD material and the template/barrier layers, leading to a 2D-3D growth mode transition, self-assembled Al y Ga 1-y N QDs with a nominal Al composition of 10% and 20% have been fabricated on Al 0.6 Ga 0.4 N. Atomic force microscopy and transmission electron microscopy measurements show high QD densities, ranging between 2x10 11 -5x10 11 cm -2 , and height and diameter distributions between 1.5 -3 nm and 5 -20 nm. LED structures including two different Al y Ga 1-y N / Al 0.6 Ga 0.4 N (0001) QD active injection current density has also been investigated and is discussed in terms of injection and recombination mechanisms in the devices.

UVB LEDs Grown by Molecular Beam Epitaxy Using AlGaN Quantum Dots

“…A typical AFM image of Al0.2Ga0.8N (n.c.) QDs grown at the surface of an Al0.7Ga0.3N layer is shown in Figure 2a. Similarly to previous results [28,33], the QD densities determined from AFM measurements have been found between 2 × 10 11 and 6 × 10 11 /cm 2 and their diameter varies between 5 and 15 nm. From previous transmission electron microscopy measurements [28], the average QD height is estimated to be of the order of the Al0.2Ga0.8N (n.c.) deposited amount ranging from 2 nm (for 8 MLs) to 3 nm (for 12 MLs), with a height distribution of ±20%.…”

Internal quantum efficiencies of AlGaN quantum dots grown by molecular beam epitaxy and emitting in the UVA to UVC ranges

“…27 Furthermore, LED structures based on QDs as active regions were recently reported using different designs, i.e. tunnel injection, 28 polar 20 or semi-polar orientations, 29 varying the QD heights 30 and compositions, 31 and have shown their potential for UV sources covering a broad wavelength range.…”

DUV LEDs based on AlGaN quantum dots

“…The main characteristics of our QD-based UV LED have been summarized in Figures 4 and 5 for the specific case of an active region made of Al0.2Ga0.8N QD since similar trends are observed for all the devices as described elsewhere. 11,21,22,24,29 The LED emission is strongly shifting into the UV at shorter wavelengths (from 349 nm down to 318 nm) as the input current density (J) increases (Figure 4(a)) and at the same time the EL spectra FWHM is strongly reduced from 63 nm down to 31 nm. In the measurements, the wavelength has been calculated as the arithmetic mean between the two wavelength values measured at full width at half maximum of each EL spectrum.…”

“…In this study, LED structures (see Figure 3(a)following a structure design similar to the ones described in refs. 11,21,22) with different Al concentrations for the AlyGa1-yN QD (i.e. with y = 0.1, 0.2, 0.3 or 0.4) were investigated.…”

“…with y = 0.1, 0.2, 0.3 or 0.4) were investigated. The QD fabrication process involved a post-growth annealing step after the deposition of an AlyGa1-yN amount of 2 nm, in order to improve the QD shape and size uniformity and avoid the formation of elongated QD 9,12,14,22 Then, a 10 nm thick Mg-doped Al0.8Ga0.2N electron blocking layer and a 10 nm thick Mg-doped Al0.7Ga0.3N layer are grown at 820°C and the structure is ended with a 30 nm thick Mg-doped GaN contact layer at a temperature of 780°C, with a Mg concentration around 5x10 19 -1x10 20 cm -3 . Reference samples made of one QD plane buried in an Al0.7Ga0.3N cladding layer for PL measurements and a surface QD plane for AFM observations (performed in tapping mode) have also been studied.…”