Semiconductor laser having co-doped distributed bragg...

Details Semiconductor laser having co-doped distributed bragg... Semiconductor laser having co-doped distributed bragg...

1998-08-31

2001-10-09

Leung, Quyen (Department: 2881)

Coherent light generators

Particular active media

Semiconductor

C372S096000

Reexamination Certificate

active

06301281

ABSTRACT:

FIELD OF THE INVENTION
The invention generally relates to the field of semiconductor devices and their fabrication. More specifically, the invention relates to light-emitting devices, such as semiconductor laser devices. The invention has particular applicability to Vertical Cavity Surface-Emitting Laser (VCSEL) devices.
BACKGROUND OF THE INVENTION
A semiconductor laser device, such as a Vertical Cavity Surface-Emitting Laser (VCSEL) device, produces monochromatic, coherent light when electrical current passes through it. Essentially, a VCSEL is made up of a layer of light-emitting material sandwiched between two reflective layers.
Heat dissipation is one of the challenges with which VCSEL designers must deal. The amount of heat generated is related to the resistance of the VCSEL, and to the amount of current the VCSEL carries. The resistance is commonly called “series resistance,” because the current flows through the layers in series. While it is desirable that the VCSEL be able to maximize the power output of the laser light by carrying as much current as possible, the heating limits the amount of current that can be carried.
Conventional approaches have been used to reduce the heat dissipation efficiency of the VCSEL structure. For instance, Kish, Jr., et al., U.S. Pat. No. 5,724,376, “Transparent Substrate Vertical Cavity Surface Emitting Lasers Fabricated by Semiconductor Wafer Bonding,” referred to below in connection with
FIG. 1
, describes a structure which employs a heat sink in proximity to the active layer.
It is also known that the resistance of the layers making up the reflective structures can be reduced by doping. This allows more current to flow, for a given amount of heating, so the light power output is increased. See, for instance, K. L. Lear et al., “Low Threshold Voltage Vertical Cavity Surface-Emitting Laser,” Electronics Letters, Vol. 29, No. 7, (Apr. 1, 1993), pp. 584-6.
Also, in P. Zhou et al., “Low Series Resistance High-Efficiency GaAs/AlGaAs Vertical-Cavity Surface-Emitting Lasers with Continuously Graded Mirrors Grown by MOCVD”, IEEE Photonics Technology Letters, Vol. 3, No. 7 (July 1991), a technique is described for reducing series resistance by grading interfaces between reflector layers.
However, there remains a need for additional new VCSEL structures, which further improve current-carrying capacity while limiting resistance, and which provide good manufacturability.
SUMMARY OF THE INVENTION
There is provided, in accordance with the invention, a semiconductor laser device which has a low series resistance and which is easily manufacturable.
Such a semiconductor laser device comprises an active layer and first and second reflective structures disposed on opposing sides of the active layer. Each of the first and second reflective structures are DBRs, and each DBR includes, respectively, (i) a first layer having a first index of refraction, and (ii) a second layer having a second index of refraction.
The two DBRs are doped, one p-type and the other n-type. While, for each DBR, the doping type is consistent, different dopants are used for the different layers of a given DBR.
In a preferred embodiment, the reflective structures are DBRs made of AlGaAs, where the Al content is varied, to vary the refractive index of the layers. Preferably, the two layers of the p-type DBR are doped with magnesium and carbon for the low- and high-refractive-index layers, respectively.


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“Low Series Resistance High-Efficiency GaAs/AIGaAs Vertical-Cavity Surface-Emitting Lasers with Continuously Graded Mirrors Grown by MOCVD”; by P. Zhou, Julian Cheng, C.F. Schaus, S. Z.. Sun, K. Zheng, E.. Armour, C. Hains, Wei Hsin, D. R. Myers, and G. A. Vawter; by IEEE Photonics Technology Letters, vol. 3., No. 7., Jul. 1991, (pp. 591-593).
“Low Threshold Voltage Vertical Cavity Surface-Emitting Laser”; by K. L.. Lear, S. A. Chalmers and K. P. Killeen; by Electronics Letters, Apr. 1, 1993, vol. 29, No. 7, (pp. 584-586).

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