Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Edge emission from 265~nm UV-C LEDs grown by MBE on bulk AlN

Shivali Agrawal, Hsin-Wei S. Huang, Debaditya Bhattacharya, Madhav Ramesh, Krzesimir Szkudlarek, Henryk Turski, Vladimir Protasenko, Huili Grace Xing, Debdeep Jena

Abstract

UV-C LEDs pseudomorphically grown by MBE on bulk AlN substrates emitting at 265 nm are demonstrated. High current density up to 800 A/cm$^2$, 5 orders of on/off ratio, and low differential on-resistance of 2.6 m$Ω\cdot$cm$^2$ at the highest current density is achieved. The LED heterostructure has a high refractive index waveguide core surrounded by n- and p-cladding layers similar to a laser diode designed for mode confinement at 270 nm to facilitate edge emission and collection of photons. Edge-emitting devices are made by cleaving the fabricated LEDs along the $m$-plane of the wurtzite crystal. Electrical injection results in emission of high energy 4.7 eV photons that are collected from the cleaved edge of the LEDs corresponding to the optical bandgap of the AlGaN active region. The contribution of power dissipation across the n- and p-regions of the diode is discussed. The n-contact resistance to n-AlGaN is identified as the largest contributor to the series resistance of the LED in the present generation of devices.

Edge emission from 265~nm UV-C LEDs grown by MBE on bulk AlN

Abstract

UV-C LEDs pseudomorphically grown by MBE on bulk AlN substrates emitting at 265 nm are demonstrated. High current density up to 800 A/cm, 5 orders of on/off ratio, and low differential on-resistance of 2.6 mcm at the highest current density is achieved. The LED heterostructure has a high refractive index waveguide core surrounded by n- and p-cladding layers similar to a laser diode designed for mode confinement at 270 nm to facilitate edge emission and collection of photons. Edge-emitting devices are made by cleaving the fabricated LEDs along the -plane of the wurtzite crystal. Electrical injection results in emission of high energy 4.7 eV photons that are collected from the cleaved edge of the LEDs corresponding to the optical bandgap of the AlGaN active region. The contribution of power dissipation across the n- and p-regions of the diode is discussed. The n-contact resistance to n-AlGaN is identified as the largest contributor to the series resistance of the LED in the present generation of devices.
Paper Structure (4 sections, 1 equation, 5 figures)

This paper contains 4 sections, 1 equation, 5 figures.

Table of Contents

  1. acknowledgments
  2. author declarations
  3. Conflict of Interest
  4. Data Availability Statement

Figures (5)

  • Figure 1: (a) Heterostructure of the LED used in this study. (b) Measured and simulated symmetric 2$\theta$-$\omega$ X-ray diffraction scans across the (002) planes. (c) Reciprocal space map across the asymmetric ($\bar{1}$05) diffractions. (d) 20 $\times$ 20 µ m$^2$ AFM scan on the surface of the LED.
  • Figure 2: (a) Secondary ion mass spectrometry (SIMS) of the LED epilayers. (b) Device schematic of the fabricated LED structure. (c) SEM image of 200 µ m cavity length devices. (d) Energy band diagram and radiative recombination rate for the LED at 5.5 V forward bias.
  • Figure 3: (a) TLM IVs of the n-contacts. The resistance is calculated at each current value using $R=V/I$ as shown in the figure. (b) TLM IVs of the p-contacts. (c) Specific contact resistivity and sheet resistance of the n- and p-contacts. (d) Linear (inset) and logarithmic diode IV characteristics and specific on resistance ($R_{\text{on}}$) at room temperature.
  • Figure 4: Voltage drop and power dissipation across different parasitic components as a function of LED current density.
  • Figure 5: (a) Current dependent electroluminescence collected from a cleaved edge of the LED. (b) Electroluminescence in logarithmic scale in a wider range from 200-400 nm. (c) Dependence of the peak wavelength and the FWHM of the EL peaks on injection current.