InAlN-based LEDs emitting in the near-UV region

Abstract

Fully functional InAlN-based ultraviolet LEDs emitting at 340–350 nm were demonstrated for the first time; detailed electrical and optical characterization is presented and discussed. Results from the measurements at pulsed conditions are in agreement with the attribution of the dominant electroluminescence peak to near-band-edge emission. The composition of the AlGaN barriers was chosen to give the same internal polarization field as that of the InAlN wells. A simulation study of this polarization-matched heterostructure shows a significant increase in the electron-hole overlap integral if compared with a standard AlGaN/AlGaN active region having the same level of carrier confinement. Limitations and problems of these preliminary devices are also presented, and possible future work aimed at increasing their efficiency is discussed.

Self-formed compositional superlattices triggered by cation orderings in m-plane Al1−xInxN on GaN

“…These results mean that average x of the nanoboards are almost homogeneous but x has remarkable inhomogeneity with the length scale shorter than a few nm. This local inhomegeneity produces remarkable E g inhomogeneity, because Al 1− x In x N alloys of low to middle x have high derivative dE g( x )/ dx value, which causes large alloy broadening 23 , 24 , 28 – 35 . In the present nanoboards, E g for x = 0.26 and 0.35 are estimated according to Refs.…”

“…For the urgent development of DUV LEDs, Al x Ga 1− x N alloys have been studied and great strides have been achieved 11 – 19 . Beyond Al x Ga 1− x N, the use of immiscible 7 , 10 , 20 – 22 Al 1− x In x N alloys is an exotic way for realizing light-emitters 23 , 24 operating in DUV to infrared wavelengths, because their bandgap energies ( E g ) cover from DUV ( E g = 6.01 eV for AlN) to infrared ( E g = 0.65 eV for InN) wavelengths. However, c -plane Al 0.82 In 0.18 N epilayers lattice-matched to GaN have been exclusively investigated as auxiliary components such as Al 0.82 In 0.18 N/GaN distributed Bragg reflectors 25 and an Al 0.82 In 0.18 N barrier for GaN heterostructure field-effect transistors 26 .…”

“…Also, because optimum film growth temperatures ( T g ) for metalorganic vapor phase epitaxy (MOVPE) of AlN (> 1600 °C) and InN (< 400 °C) are significantly different, Al 1- x In x N alloys suffer from kinetic phase separation due to instantaneous evaporation of In or InN from the surface 7 . Consequently, there have been few reported results on a near-band-edge (NBE) emission of Al 1− x In x N films 5 , 23 , 28 – 34 and QWs 24 , 35 , and the NBE emission exhibited large full-width at half-maximum (FWHM) value of a few hundred meV 5 , 23 , 24 , 28 – 35 and Stokes’ shifts (SSs) larger than several hundred meV or nearly 1 eV, which is the energy difference between the absorption and emission. From a different perspective, large SS 29 , 30 , 32 , 34 , weak thermal quenching 23 , 32 , and morphology-insensitive cathodoluminescence (CL) intensity mapping images 23 for the NBE emission owing to short minority-carrier (hole) diffusion length ( L p ) likely suggest that the NBE emission originates from certain localized states.…”

“…Although the magnitude of polarization ( ) was not unity, the electric field ( E ) component of the light was polarized parallel to the c -axis ( E // c ). However, little is known about the luminescence mechanisms of Al 1− x In x N alloys 5 , 23 , 24 , 28 – 35 and it is worth clarifying the reason why Al 1− x In x N exhibits defect-tolerant radiation probability. In this article, two distinct length-scale cation orderings are exemplified to explain the appearance and self-formation sequence of compositional superlattices (CSLs) in m -plane Al 0.72 In 0.28 N films, in which excitons are confined in Al 0.70 In 0.30 N layers.…”

Polarization Modulation at Last Quantum Barrier for High Efficiency AlGaN-Based UV LED

“…Nevertheless, high quality InAlN LEDs and power devices with lower indium compositions have been achieved. Anna et al reported the In0.14Al0.86N /AlN/GaN high electron mobility transistor (HEMT) [44] and Pietro et al fabricated the UVA LED with In0.14Al0.86N polarization matched quantum well [45]. Thus, we believe our design could effectively improve the polarization issue in AlGaN-based UV LED without introducing complex structures and growth techniques.…”