Status of Nitride Based Light Emitting and Laser Diodes on SiC
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K.Doverspike, G.E.Bulman, S.T.Sheppard, H.S.Kong, M.Leonard, H.Dieringer, T.W.Weeks, Jr., J.Edmond, J.D.Brown*, J.T.Swindle*, J.F.Schetzina*, Y-K Song**, M.Kuball** and A.Nurmikko**, Cree Research, Inc, 2810 Meridian Parkway, Durham NC 27713. *Department of Physics, North Carolina State University, Raleigh, NC 27659. "**Brown University, Providence RI 02912. [email protected]
ABSTRACT Single crystal thin films with compositions from the A1N-InN-GaN system were grown via metal-organic chemical vapor deposition (MOCVD) on single crystal 6H-SiC substrates. Blue light emitting (LED) and laser diode (LD) structures were fabricated. The conducting buffer layer LEDs employed an AlGaN buffer layer which provides a conduction path between SiC and the active device region. The external quantum efficiency of the LEDs was 3% at 20 mA- 3.6V and peak emission wavelength of 430 nm. Violet and blue LDs were fabricated and consisted of an 8-well InGaN/GaN multiple
quantum well (MQW) active region in a separate confinement heterostructure (SCH) design. Lasing was obtained both on structures using an insulating buffer layer, and also on structures using a conducting buffer layer. The resulting lasers operated at room temperature using pulsed and continuous wave operation with an emission wavelength of 404-435 rim. The lowest threshold current density obtained for lasing was 11 kA/cm 2. INTRODUCTION The development of super-bright blue and green LEDs and LDs has proved the viability of the AIN-InN-GaN alloy system. Three commercial sources for these LEDs, Nichia Chemical, Toyoda Gosei and Hewlett Packard, employ sapphire substrates which have a 16% lattice mismatch with GaN and requires two top side contacts to pass current through the p-n junction. These devices employ an InGaN quantum well layer as the emitter. Nakamura[1] of Nichia Chemical demonstrated InGaN single quantum well (SQW) LEDs grown on sapphire emitting from violet to orange. The external quantum 1169 Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
efficiency of these devices are the highest recorded for the InGaN system. As the indium fraction of the InGaN SQW increases, the efficiency of the LED decreases from 10% at 400 tim (-14% In) to 1.2% at 600 nm (-77% In). From this research, Nichia Chemical released blue and green SQW LEDs in production in 1996. The blue LED with an active layer composition of InO. 36 Ga 0 .64 N has a typical output of 2.5 mW at a peak wavelength of 470 tim and full width half maximum (FWHM) of 30 nm. The green version, with an active layer composition of In 0 .53 Ga 0 .47N, has a typical output of 1.5 mW at a peak wavelength of 525 nm and a bandwidth of 40 nm. Koike et. al.[2] of Toyoda Gosei Co. has demonstrated an asymmetric double heterostructure InGaN/GaN MQW LEDs. The active layer of the blue LED has a typical FWHM of approximately 40nm and a peak wavelength at 460nm. The green MQW LED has a FWHM of about 45nm and a peak wavelength at 520nm. Nakamura et. al.[3] also has demonstrated room temperature conti
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