Abstract
The impact of plasma etching on the formation of low-resistance n-contacts on the AlGaN:Si current spreading layer during the chip fabrication of ultraviolet light-emitting diodes (UVLEDs) emitting at 265 nm is investigated. A two-step plasma etching process with a first rapid etching using BCl3/Cl2 gas mixture and a second slow etching step using pure Cl2 gas has been developed. The etching sequence provides smooth mesa side-walls and an n-AlGaN surface with reduced surface damage. Ohmic n-contacts with a contact resistivity of 3.5 × 10−4 Ωcm2 are obtained on Si-doped Al0.65Ga0.35N layers and the operating voltages of the UVC LEDs were reduced by 2 V for a current of 20 mA.
Highlights
AlGaN-based deep ultraviolet light-emitting diodes (UV LEDs) are promising devices that could replace mercury discharge lamps in various applications including sterilization, water purification, medical diagnostics, phototherapy, and UV curing [1,2,3]
We report on the effects of the BCl3 to Cl2 gas flow ratio and radio frequency (RF) power during the inductively coupled plasma (ICP)-reactive ion etching (RIE) plasma etching of n-Al0.65Ga0.35N:Si on the etch rate and the smoothness of fabricated mesa edges
The rough sidewalls of the etched mesa were observed independent of the ICP power or the RF power
Summary
AlGaN-based deep ultraviolet light-emitting diodes (UV LEDs) are promising devices that could replace mercury discharge lamps in various applications including sterilization, water purification, medical diagnostics, phototherapy, and UV curing [1,2,3]. Stoichiometry of the AlGaN materials, and damage the crystal structure [6] All these effects are known to influence the performance of the electrical contact. A two-step plasma etching process has been reported for GaN which involves a final etch step with BCl3/Cl2 and Cl2 gases at low power to reduce crystal damage. We report on the effects of the BCl3 to Cl2 gas flow ratio and RF power during the ICP-RIE plasma etching of n-Al0.65Ga0.35N:Si on the etch rate and the smoothness of fabricated mesa edges. A two-step etch process including a final etching with Cl2 at low RF power will be shown to provide the a smooth surface and the a low resistivity for vanadium-based contacts deposited thereon. The approach described contributes to gradually increasing the low efficiency of UVC LEDs and to improve the still limited applicability of the components
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