Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-11-03
2001-04-17
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S045013
Reexamination Certificate
active
06219365
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains generally to the field of semiconductor diode lasers and particularly to semiconductor lasers emitting at wavelengths in the range of 700 nm to 800 nm.
BACKGROUND OF THE INVENTION
Semiconductor diode lasers are formed of multiple layers of semiconductor materials. The typical semiconductor diode laser includes an n-type layer, a p-type layer and an undoped active layer between them such that when the diode is forward biased electrons and holes recombine in the active region layer with the resulting emission of light. The layers adjacent to the active layer typically have a lower index of refraction than the active layer and form cladding layers that confine the emitted light to the active layer and sometimes to adjacent layers. Semiconductor lasers may be constructed to be either edge emitting or surface emitting. In an edge emitting Fabry-Perot type semiconductor laser, crystal facet mirrors are located at opposite edges of the multi-layer structure to provide feedback reflection of the emitted light back and forth in a longitudinal direction, generally in the plane of the layers, to provide lasing action and emission of laser light from one of the facets. Another type of device, which may be designed to be either edge emitting or surface emitting, utilizes distributed feedback structures rather than conventional facets or mirrors, providing feedback for lasing as a result of backward Bragg scattering from periodic variations of the refractive index or the gain or both of the semiconductor laser structure.
High output power diode lasers with wavelengths in the 730-780 nm range are needed for a variety of applications ranging from laser printing and optical recording to cancer treatments such as photodynamic therapy. For wavelengths less than 840 nm, typical laser structures use AlGaAs in the active region, which can result in long-term reliability problems. For devices intended to operate with emission wavelengths less than 780 nm, the high aluminum content of the Al
x
Ga
1−x
As active layer (x>0.1) required to obtain light emission at such wavelengths makes reliable high-power operation increasingly difficult to achieve. The high surface recombination velocity for AlGaAs leads to catastrophic optical mirror damage (COMD) at relatively low power densities. Even small Al concentrations (e.g., x≈0.07-0.10) lead to significant reductions in internal power densities at COMD. Using a specially processed oxygen gettered aluminum source for the metal-organic chemical-vapor deposition (MOCVD) growth process, AlGaAs active-layer devices (100 &mgr;m-wide emission aperture) have been reported with continuous wave (cw) output powers of 540 mW at an emission wavelength of 715 nm. P. L. Tihanyi, F. C. Jain, M. J. Robinson, J. E. Dixon, J. E. Williams, K. Meehan, M. S. O'Neill, L. S. Heath, and D. M. Beyea, IEEE Photonics Technol. Lett. 6, 775 (1994). More recently, compressively strained AlGaInAs active-layer lasers have been reported in the 730 nm wavelength range demonstrating 2.2 W cw output powers from broad-stripe (100 &mgr;m-wide) devices. M. A. Emanuel, J. A. Skidmore, M. Jansen and R. Nabiev, IEEE Photonics Technol. Lett. 9, 1451 (1997). Although high output powers have been obtained from the AlGa(In)As active-layer devices, long-term reliability is still an open question because, even if the mirror facets are passivated, since defects in the bulk of the active region material cause device degradation. For such devices emitting at wavelengths in the range of 700 nm to 780 nm there is no extensive lifetest data and high power devices are not commercially available.
The lower surface recombination velocity of InGaAsP compared with AlGaAs leads to a corresponding reduction in facet-temperature rise during high-power cw operation. D. Z. Garbuzov, N. Yu. Antonishkis, A. D. Bondarev, A. B. Gulakov, S. N. Zhigulin, N. I, Katsavets, A. V. Kochergin, and E. V. Rafailov, IEEE J. Quantum Electron. QE-27, 1531 (1991). Tensile-strained (In) GaAsP active-layer lasers have been reported operating in the 700-800 nm wavelength range. D. P. Bour, D. W. Treat, K. J. Beernink, R. L. Thornton, T. L. Paoli, and R. D. Bringans, IEEE Photonics Technol. Lett. 6, 1283 (1994). However, little is known about the properties of compressively strained quantum-well lasers in this wavelength region. Compressively strained active layers have been reported with emission at 980 nm, D. F. Welch, W. Streifer, C. F. Schaus, S. Sun and P. L. Gourley, Appl. Phys. Lett. 56, 10 (1990); at 1.3 &mgr;m, P. J. A. Thijs, L. F. Tiemeijer, J. J. M. Binsma and T. van Dongen, IEEE J. Quantum Electron. QE-30, 477 (1994); and at 1.55 &mgr;m, A. Mathur and P. Dapkus, IEEE J. Quantum Electron. QE-32, 3223 (1996).
SUMMARY OF THE INVENTION
In accordance with the invention, a semiconductor laser is provided which may be constructed to emit light in the wavelength range of about 700 nm to 800 nm, and for some applications at longer wavelengths, utilizing an aluminum free active region layer. Because the active region is aluminum free, much higher internal power densities at the point of catastrophic optical mirror damage are obtained as compared to conventional semiconductor laser structures which require the presence of aluminum in the active region in order to provide emission in the 700 nm to 800 nm range. The laser structures of the invention are capable of operating at high power with high reliability with the long lifetimes required for commercially feasible lasers.
The semiconductor laser of the invention includes a crystalline semiconductor substrate (e.g., GaAs or AlGaAs), an epitaxial structure on the substrate including a layer with an active region at which light emission occurs, confinement layers adjacent the active region layer, cladding layers adjacent the confinement layers, edge faces, electrodes by which voltage can be applied across the epitaxial structure and the substrate, and feedback structures to provide optical feedback for lasing in the active region layer. The active region layer is aluminum free and comprises at least one compressively strained InGaAsP quantum well surrounded by transitional layers of, e.g., InGaP, InGaAsP, or GaAsP, with the active region selected to emit light at a wavelength in the range of about 700 nm to 800 nm. The selection of the wavelength at which the active region emits may be determined by selection of the relative composition of the material of the active region and the width of the quantum well. A preferred structure in accordance with the invention utilizes high band-gap InGaAlP cladding layers and confinement layers to suppress carrier leakage.
It is also preferred in accordance with the invention that the epitaxial structure be grown on a substrate surface off orientation with respect to a major crystalline plane, preferably at least 5° off orientation, e.g., on (100) substrates misoriented 5° to 20° toward <111>. Growth of the epitaxial structure on highly misoriented substrates disorders the InGaAlP layers, increasing the band-gap significantly (by about 70 meV). This larger band-gap further reduces carrier leakage from the quantum well, with corresponding very low temperature sensitivity for such devices constructed for wavelength emissions of at least 700 nm. The strong carrier confinement allows high cw power to be achieved without substantially affecting other device parameters.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5222090 (1993-06-01), Serreze
patent: 5389396 (1995-02-01), Razeghi
patent: 5889805 (1999-03-01), Botez et al.
patent: 6028874 (2000-02-01), Wada et al.
patent: 6028875 (2000-02-01), Knight et al.
patent: 6127691 (2000-10-01), Fukunaga et al.
D.P. Bour, et al., “Tensile-Strained AlGaAsP-and InGaAsP-(AlGa)0.5In0.5P Quantum Well Laser Diodes for TM-Mode Emission in the Wavelength Range 650 <&lgr;< 850 nm,” IEEE Photonics Technology L
Al-Muhanna Abdulrahman
Botez Dan
Mawst Luke J.
Wade Jerome Kent
Davie James W.
Foley & Lardner
Wisconsin Alumni Research Foundation
LandOfFree
High performance aluminum free active region semiconductor... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High performance aluminum free active region semiconductor..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High performance aluminum free active region semiconductor... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2540107