Efficient Green Emission from Wurtzite Al_xIn_1–xP Nanowires

Abstract

Direct band gap III–V semiconductors, emitting efficiently in the amber–green region of the visible spectrum, are still missing, causing loss in efficiency in light emitting diodes operating in this region, a phenomenon known as the “green gap”. Novel geometries and crystal symmetries however show strong promise in overcoming this limit. Here we develop a novel material system, consisting of wurtzite AlxIn1–xP nanowires, which is predicted to have a direct band gap in the green region. The nanowires are grown with selective area metalorganic vapor phase epitaxy and show wurtzite crystal purity from transmission electron microscopy. We show strong light emission at room temperature between the near-infrared 875 nm (1.42 eV) and the “pure green” 555 nm (2.23 eV). We investigate the band structure of wurtzite AlxIn1–xP using time-resolved and temperature-dependent photoluminescence measurements and compare the experimental results with density functional theory simulations, obtaining excellent agreement. Our work paves the way for high-efficiency green light emitting diodes based on wurtzite III-phosphide nanowires.

Forbidden Band‐Edge Excitons of Wurtzite‐GaP: A Theoretical View

“…The position of the lowest 2 p exciton predicted theoretically agrees well with the 2.14 eV emission energy found experimentally for the so‐called A exciton . However, also the two other series approaching the positions of the B and C excitons found in photoluminescence as well as photoluminescence excitation (PLE) spectroscopy .…”

“…Indeed, wurtzite‐GaP but also wurtzite‐AlAs NWs have been grown and investigated . Moreover, Al x In 1− x P alloys have been grown in wurtzite geometry in core‐shell or unique NWs . The optical studies show a direct band gap, but the strength of the optical band gap transitions remains under discussion.…”

“…Most interesting are phosphide‐based wurtzite semiconductors, which are indirect in zinc‐blende crystal structure under ambient conditions. At room temperature, in wurtzite geometry they show intense photoluminescence in the yellow‐green region at 594 nm wavelength ( wz ‐GaP) or between the near infrared (875 nm) and “pure” green (555 nm) spectral region varying the Al content in wz ‐Al x In 1− x P between x = 0 and x = 0.4 . The strong emission from wz ‐GaP and wz ‐Al x In 1− x P (with intermediate Al content) is not understood in terms of the bulk band structures.…”

Compositional and structural engineering of inorganic nanowires toward advanced properties and applications

“…As shown in Figure J, the Al 0.25 In 0.75 P hexagonal nanostructure displayed a distinct emission intensity distribution due to the compositional difference, with the main wavelength at 615 nm. A change in the x value resulted in effective emission wavelength modulation, by which a strong light emission at room temperature between the near‐infrared 875 nm (1.42 eV) wavelength and the “pure green” 555 nm (2.23 eV) wavelength was achieved (Figure L) . These results imply that Al 0.25 In 0.75 P is a good supplement to III‐V light‐emitting compounds.…”

“…A change in the x value resulted in effective emission wavelength modulation, by which a strong light emission at room temperature between the near-infrared 875 nm (1.42 eV) wavelength and the "pure green" 555 nm (2.23 eV) wavelength was achieved ( Figure 5L). 104 These results imply that Al 0.25 In 0.75 P is a good supplement to III-V light-emitting compounds.…”