Molecular-beam epitaxy (MBE) has several advantages over metal-organic chemical vapor deposition (MOCVD). For example, films with lower point defect concentration have been achieved. Furthermore, no post-growth activation of Mg dopants is required and Mg memory effects are negligible, which leads to sharp Mg doping profiles. However, MBE grown light emitting diodes (LEDs) are usually reported to have low output power, limited to a few tens of mW.

The aim of our work is to investigate the key steps to improve the brightness of MBE-LEDs. Our films are grown in a Varian Gen II MBE system equipped with standard effusion cells for Ga (2), In, Mg and Si. Active nitrogen is supplied by an EPI Unibulb radio frequency (rf) plasma source. The MBE structures are grown on 2 µm thick GaN:Si templates grown by MOCVD on c-plane sapphire.

Measurements of the absolute output power and lifetime testing were performed on standard epoxy packaged, no flip-chip devices. For a 200 mm diode, the highest power was 0.28 mW at 20 mA which is among the best values ever reported for MBE-LEDs. The lifetime testing of 200 µm diodes was performed under a current density of 33.25 A/cm² for 500 hours. The lifetime testing did not show any degradation of the output power or driving voltage. Current experiments are directed towards further improvement of the output power using low dislocation density templates and AlGaN electron blocking layer between the active region and the p-GaN.

	Electroluminescence spectra of a 200 µm diode under forward currents of 10, 20, …, 100 mA.
	Light versus current curve for LEDs of various diode sizes

Last updated Tuesday, March 11, 2003
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