Interband tunneling for hole injection in III-nitride ultraviolet emitters

Abstract

Low p-type conductivity and high contact resistance remain a critical problem in wide band gap AlGaN-based ultraviolet light emitters due to the high acceptor ionization energy. In this work, interband tunneling is demonstrated for non-equilibrium injection of holes through the use of ultra-thin polarization-engineered layers that enhance tunneling probability by several orders of magnitude over a PN homojunction. Al 0.3 Ga 0.7 N interband tunnel junctions with a low resistance of 5.6×10 -4 Ω cm 2 were obtained and integrated on ultraviolet light emitting diodes. Tunnel injection of holes was used to realize GaN-free ultraviolet light emitters with bottom and top n-type Al 0.3 Ga 0.7 N contacts. At an emission wavelength of 327 nm, stable output power of 6 W/cm 2 at a current density of 120 A/cm 2 with a forward voltage of 5.9 V was achieved. This demonstration of efficient interband tunneling introduces a new paradigm for design of ultraviolet light emitting diodes and diode lasers, and could enable higher efficiency and lower cost ultraviolet emitters.

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

“…[267] The issue of light extraction and hole transport might also be addressable through the use of interband tunnel junctions. [206] New device designs and material deposition approaches to manage the strain and polarization in UWBG heterostructures are also being explored with some initial success. To overcome the bulk AlN substrate issue, new approaches are needed to create thick and low-defect-density free-standing AlN substrates to replace inferior but readily available UV-C transparent substrates such as sapphire.…”

Tunnel junction enhanced nanowire ultraviolet light emitting diodes

“…In this work, we integrate polarization-engineered tunnel junctions (TJs) [16]- [18] within the nanowire UV LEDs. The TJs efficiently inject holes into the p-type graded layer utilizing interband tunneling, thereby converting the bottom contact from p-type to n-type.…”

“…Furthermore, the efficiency droop in these nanowire LEDs is greatly reduced, which we attribute to enhanced non-equilibrium hole concentration due to interband tunneling. [16]- [18] is deposited followed by a doubly graded polarization doped UV LED structure as described earlier [9], [10], [13]. The nanowire heterostructures are grown from self-assembled catalyst free nanowires using a two-step [19]- [21] dynamic growth process byplasma assisted molecular beam epitaxy in a Veeco GEN 930 system.…”

Enhanced light extraction in tunnel junction-enabled top emitting UV LEDs

“…The valence band edge in the p-AlGaN side is aligned with the conduction band edge in the n-AlGaN side within a few nanometers, forming an almost broken gap alignment with reduced interband tunneling barrier height across the thin InGaN layer. [17][18][19] The tunnel junction (TJ) structure enables low-resistance contact to the p-AlGaN layer with a transparent n-AlGaN top contact layer. Using this approach, photons from the active region can be extracted directly from the top surface with minimal optical loss from the thin InGaN layer.…”

“…8,9 The tunneling injected UV LED structure mitigates the absorption loss issues in UV LEDs, since the InGaN interband tunneling layer used (< 4 nm) is significantly thinner than typical p-GaN capping layers (> 20 nm). 17 This makes it possible to achieve UV light extraction efficiency comparable to the visible counterparts, and reduces the complexity and cost of device fabrication. Engineering the active region design could lead to preferential surface emission instead of side-emission for deep UV LEDs emitting longer wavelengths than 240 nm.…”