APPLIED PHYSICS LETTERS, cilt.110, 2017 (SCI İndekslerine Giren Dergi)
We report on tunnel-injected deep ultraviolet light emitting diodes (UV LEDs) configured with a polarization engineered Al0.75Ga0.25 N/In0.2Ga0.8N tunnel junction structure. Tunnel-injected UV LED structure enables n-type contacts for both bottom and top contact layers. However, achieving Ohmic contact to wide bandgap n-AlGaN layers is challenging and typically requires high temperature contact metal annealing. In this work, we adopted a compositionally graded top contact layer for non-alloyed metal contact and obtained a low contact resistance of rho(c) = 4.8 x 10(-5) Omega cm(2) on n-Al(0.75)G(a0.25)N. We also observed a significant reduction in the forward operation voltage from 30.9V to 19.2V at 1 kA/cm(2) by increasing the Mg doping concentration from 6.2 x 10(18) cm(-3) to 1.5 x 10(19) cm(-3). Non-equilibrium hole injection into wide bandgap Al0.75Ga0.25N with Eg>5.2 eV was confirmed by light emission at 257 nm. This work demonstrates the feasibility of tunneling hole injection into deep UV LEDs and provides a structural design towards high power deep-UV emitters. Published by AIP Publishing.