Highly Conductive n-Al0.65Ga0.35N Grown by MOCVD Using Low V/III Ratio

Abstract

Highly conductive silicon-doped AlGaN and ohmic contacts are needed for deep-UV LEDs and ultrawide bandgap electronics. We demonstrate improved n-Al0.65Ga0.35N films grown by metal–organic chemical vapor deposition (MOCVD) on sapphire substrates using a low V/III ratio (V/III = 10). A reduced V/III ratio improves repeatability and uniformity by allowing a wider range of silicon precursor flow conditions. AlxGa1−xN:Si with x > 0.5 typically has an electron concentration vs. silicon concentration trend that peaks at a particular “knee” value before dropping sharply as [Si] continues to increase (self-compensation). The Al0.65Ga0.35N:Si grown under the lowest V/III conditions in this study does not show the typical knee behavior, and instead, it has a flat electron concentration trend for [Si] > 3 × 1019 cm−3. Resistivities as low as 4 mΩ-cm were achieved, with corresponding electron mobility of 40 cm2/Vs. AFM and TEM confirm that surface morphology and dislocation density are not degraded by these growth conditions. Furthermore, we report vanadium-based ohmic contacts with a resistivity of 7 × 10−5 Ω-cm2 to AlGaN films grown using a low V/III ratio. Lastly, we use these highly conductive silicon-doped layers to demonstrate a 284 nm UV LED with an operating voltage of 7.99 V at 20 A/cm2, with peak EQE and WPE of 3.5% and 2.7%, respectively.

Contact Engineering of III-Nitrides and Metal Schemes toward Efficient Deep-Ultraviolet Light-Emitting Diodes

“…The fabricated device shows the emission wavelength of 272 nm and a full width at half-maximum of 11.6 nm. Figure b shows the forward voltage (@20 mA) versus wavelength values for recently reported DUV LEDs with optimized n-contact, ,,,− ,− indicating the advantages of the contact engineering strategy. The detailed performance parameters for recently reported DUV LEDs with optimized n-contact are summarized in Table S1.…”

Towards Efficient Electrically-Driven Deep UVC Lasing: Challenges and Opportunities

“…Figure 3 shows Hall’s electron concentrations in the n + -AlGaN alloys as a function of incorporated Si-donor concentrations using MOVPE and MBE growth techniques [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]. One can see that the maximum electron concentration achieved by both MOVPE and MBE to date is ~4 × 19 19 cm −3 [ 56 , 59 ].…”

“…Figure 3 shows Hall’s electron concentrations in the n + -AlGaN alloys as a function of incorporated Si-donor concentrations using MOVPE and MBE growth techniques [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]. One can see that the maximum electron concentration achieved by both MOVPE and MBE to date is ~4 × 19 19 cm −3 [ 56 , 59 ]. Most of the reported MOVPE data show a dramatic drop of the electron density starting from [Si] = ~4−5 × 19 19 cm −3 , attributed to the massive generation of point defects, of which the origin is still under debate [ 55 ].…”

“…Most of the reported MOVPE data show a dramatic drop of the electron density starting from [Si] = ~4−5 × 19 19 cm −3 , attributed to the massive generation of point defects, of which the origin is still under debate [ 55 ]. Optimization of the growth temperature and the V/III ratio aimed at reduction of the point defect density enables avoiding of the drop [ 55 , 56 ]. However, further increase in the electron density with Si-donor concentration has not been achieved yet.…”

“…The arrow in the left plot indicates the decrease of the electron concentration with the AlN molar fraction reported by Nakarmi et al [ 52 ]. Inset legends on both plots indicate the percentage of Al in the AlGaN alloys [ 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ].…”