Improved AlGaInP-based red (670–690 nm) surface-emitting lasers with novel C-doped short-cavity epitaxial design

Abstract

A modified epitaxial design leads to straightforward implementation of short ͑1 ͒ optical cavities and the use of C as the sole p-type dopant in AlGaInP/AlGaAs red vertical-cavity surface-emitting lasers ͑VCSELs͒. Red VCSELs fabricated into simple etched air posts operate continuous wave at room temperature at wavelengths between 670 and 690 nm, with a peak output power as high as 2.4 mW at 690 nm, threshold voltage of 2.2 V, and peak wallplug efficiency of 9%. These values are all significant improvements over previous results achieved in the same geometry with an extended optical cavity epitaxial design. The improved performance is due primarily to reduced optical losses and improved current constriction and dopant stability. © 1995 American Institute of Physics.AlGaInP materials technology has steadily advanced over the past several years, leading to high-performance edge-emitting lasers ͑EELs͒ 1 and red vertical-cavity surfaceemitting lasers ͑VCSELs͒. 2,3 Relative to the AlGaInP system, AlGaAs benefits from improved index contrast, reduced electrical and thermal resistivity, a more mature processing technology, and the ability to use carbon as the p-type dopant for superior dopant control and stability. 4 However, integrating AlGaInP-based active regions with C-doped AlGaAsbased DBRs are made difficult by poor carrier transport into the AlGaInP active region and the inability to use C for p-doping in AlGaInP alloys. Previous reports of AlGaInP/ AlGaAs heterostructure laser diodes have all employed Zn or Mg doping on the p side of the junction to improve hole injection, 5,6 eliminating a potential key advantage of the use of AlGaAs and further complicating dopant diffusion characteristics. 7,8 Such difficulties have led to implementation of relatively thick ͑8 ͒ optical cavities in red VCSELs 6 at the cost of increased optical loss and thermal resistivity and less efficient current constriction.In the present letter we investigate a modified epitaxial design that not only enables straightforward implementation of short ͑1 wave͒ optical cavities but also the use of carbon as the sole p-type dopant in AlGaInP/AlGaAs-based red EELs and VCSELs. This approach better utilizes the advantages of AlGaAs materials technology in the device structure and eliminates the problems with Zn and Mg doping entirely. The resulting VCSELs benefit from considerable simplification of the growth and doping and significantly improved performance. This work also represents the first successful use of C as the only p-type dopant in AlGaInP-based red laser diodes.All the devices described in this work were grown using low-pressure metalorganic vapor phase epitaxy ͑MOVPE͒ in a horizontal quartz reaction chamber as described previously. 9 The dopants include Si ͑from disilane͒ for n-type AlGaAs and AlGaInP, C ͑from CC14͒ for p-type AlGaAs͑P͒, and Zn ͑from dimethylzinc͒ and Mg ͑from biscyclopentadienyl magnesium͒ for p-type AlGaInP. Several different laser heterostructures were investigated, as described. The EEL quantum well ͑QW͒ active r...

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