A. Oster, M. Zorn, K. Vogel, J. Fricke, J. Sebastian, W. John, M. Weyers, G. Tränkle

Published in:

Proc. SPIE, vol. 4286, pp. 148-155 (2001).

Abstract:

Red VCSELs for emission wavelengths near 650 nm find applications in emerging technologies such as plastic-fiber-based data communication. However, these devices are challenging due to low band offsets and high electrical and thermal resistivity of especially the p-DBR. The paper presents the optimization of p-DBR and QW design for the reduction of the series resistance and the threshold current density.
VCSEL structures were grown using MOVPE and processed to air-post mesas. The resistance of the p:DBR mirrors was optimized using different dopants and interfaces. By changing from Zn doping and abrupt interfaces to the dopant C and introducing graded interfaces the differential resistance decreased. Due to a relative shift across the wafer between the DBR stop-band and gain-peak wavelength defined by the MQW active region, devices are available with lasing wavelengths between 638 nm and 662 nm in pulsed-mode operation. Threshold current densities of 3.6 kA/cm² at 650 nm are measured.
For improving device parameters a current aperture was processed by selective wet oxidation of Al_xGa_1-xAs with varying x. Cw laser operation is achieved for wavelengths between 644 nm and 657 nm at 10°C ambient temperature. With threshold currents under 4 mA maximum cw powers of 160 µW are obtained at wavelengths of 657 nm and 650 nm.

Keywords:
vertical-cavity surface-emitting lasers, VCSEL, visible, red, 650 nm, distributed Bragg reflector, DBR, MOVPE, selective oxidation

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