Digital Alloys of AlN/AlGaN for Deep UV Light Emitting Diodes

Abstract

We report a systematic study of the optical and electrical properties of deep ultraviolet light emitting diodes based on digital alloy structures of AlN/Al0.08Ga0.92N grown by gas source molecular beam epitaxy with ammonia. Digital alloys are formed by short period superlattices consisting of Al0.08Ga0.92N wells, 0.50 or 0.75 nm thick, and AlN barriers, 0.75 to 1.5 nm thick. For digital alloys with effective bandgap of 5.1 eV, average AlN composition 72%, we obtain room temperature electron concentrations up to 1×1019 cm-3 and resistivity of 0.005 Ω·cm and hole concentrations of 1×1018 cm-3 with resistivity of 6 Ω·cm. Light emitting diodes based on digital alloys are demonstrated operating in the range of 250 to 290 nm.

Final LDRD report : science-based solutions to achieve high-performance deep-UV laser diodes.

“…using GS-MBE. 24 This work extends the range of AlGaN based Mg-SL structures grown by MOVPE that exhibit hole conduction to Al compositions of 0.74, which is a suitable composition for cladding layers in ~280 nm laser diode structures. Further studies to quantitatively assess vertical transport properties and optical losses in Mg-SPSL will more clearly delineate the potential of these structures for vertical injection deep-UV optoelectronic devices.…”

“…21 In further studies, Nikishin and co-workers have extended the concept of Mg-doped SLs to significantly higher Al compositions. [22][23][24][25] Unlike previous work, they employed gas-source molecular beam epitaxy (GS-MBE) to fabricate short-period superlattice (SPSL) structures consisting of monolayer thick layers of AlN and Al x Ga 1-x N with a large difference in Alcomposition (>0.90) between epilayers. They reported P-type conductivity in Mg-doped SPSL structures consisting of 7.5-15 Å thick AlN barrier layers and 5-7.5 Å thick Al x Ga 1-x N (0.05 < x < 0.10) well layers.…”

“…This range of hole concentration is similar to that reported by Nikishin. 24 For selected samples, Hall measurements were made as a function of temperature to investigate the ionization energy of Mg acceptors in SPSL structures. Since hole concentrations were not reliably measured over the temperature range investigated, we show in Figure 14(a) temperature dependent resistivity data for two MgSPSLs and a p-GaN epilayer.…”

Activation energy of Mg in Al0.25Ga0.75N and Al0.5Ga0.5N

“…Several groups have already reported UV LEDs [1][2][3][4][5][6][7]. However, UV LEDs show much lower efficiency compared with blue LEDs.…”

Growth kinetics of AlxGa1–xN layers (0 < x < 1) in plasma‐assisted molecular beam epitaxy

“…1 Introduction Significant progress in fabrication of AlGaN-based light-emitting devices for the deep UV wavelength range by different growth techniques, mainly metal-organic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE), has been achieved recently [1][2][3]. MBE technique provides unique opportunities for accurate control of epitaxial growth with a sub-monolayer resolution, as well as a possibility to grow AlGaN epilayers at low temperatures in hydrogen free atmosphere, which facilitates using of low Mg fluxes for the successful p-type doping without post growth activation [4].…”