Optical Properties of AlGaN Quantum Well Structures
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F99W11.35 Downloaded from https://www.cambridge.org/core. IP address: 212.60.21.170, on 19 Aug 2020 at 08:59:59, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300004956
from the near band-edge. Then we fabricated AlGaN-MQWs consisting of wide bandgap AlGaN (Al content: 53-100%) barriers. The well thickness dependence of PL properties is systematically investigated. We show efficient emission around 230 nm obtained from the AlN/AlGaN MQWs. Finally, the PL intensities are compared between AlGaN MQWs with various Al content of AlGaN barriers, and InGaN and GaN QWs. EXPERIMENTS AND DISCUSSIONS The samples were grown at 76 Torr on the Si-face of an on-axis 6HSiC(0001) substrate, by a conventional horizontal-type MOVPE system. As precursors ammonia (NH3), trimethylaluminum (TMAl), and trimethylgallium (TMGa) were used with H2 as carrier gas. N2 gas was independently supplied by a separate line in order to control the gas flow. Typical gas flows were 2 standard liters per minute (SLM), 2 SLM, and 0.5 SLM for NH3, H2, and N2, respectively. The molar fluxes of TMGa and TMAl for the growth of AlxGa1-xN (x=0.11-1) were 38 and 2.6-45 µmol/min, respectively. At this condition, the growth rate of Al0.11Ga0.89N, Al0.40Ga0.60N and AlN were approximately 2.4, 1.0 and 0.4 µm/h, respectively. The substrate temperature measured with a thermocouple located at the substrate susceptor during the growth was 1140 °C for all layer. All samples were undoped.
Photoluminescence of AlxGa1-xN 1.2
PL Intensity(a.u.)
x=0.95
0.77
0.60 0.53 0.45 0.35
0.20
0.11
1 0.8
(a)
0.6 0.4 0.2 0 200
220
240
260
280
300
Wavelength λ(nm)
320
340
360
150
FWHM (meV)
Measured at 77K 120 90
(b)
60 30 0 200
220
240
260
280
300
Wavelength λ(nm)
320
340
360
Figure 1. PL spectra of AlxGa1-xN (x=0.11-0.95) films grown on 6H-SiC measured at 77 K.
F99W11.35 Downloaded from https://www.cambridge.org/core. IP address: 212.60.21.170, on 19 Aug 2020 at 08:59:59, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300004956
PL Intensity (a.u.)
1 x=0.95 0.90
0.88 0.86
0.8 0.6 0.4 0.2 0 210
220
230
Wavelength λ(nm)
240
Figure 2. PL spectra of high Al content AlxGa1-xN (x=0.86-0.95) films measured at 77 K. At first, we show the optical properties of high Al content AlGaN alloy. Figure 1 shows (a) the PL spectra and (b) full width at half maximum (FWHM) of the PL peak of AlGaN films measured at 77 K. The AlGaN alloy was grown directly on a very thin (∼5 nm) AlN layer deposited on SiC. Figure 2 also shows the PL spectra of high Al content AlGaN (Al content is 85-95%). The thickness of AlGaN film was approximately 250 and 400 nm for AlN and Al0.11Ga0.89N, respectively. As seen in Fig. 1 and 2, single peak spectra were obtained for Al contents of 0.11-0.95 emitting from near band edge. The yellow emission around 500-550 nm was negligible even for high Al content AlGaN. The phonon-replic
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