Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-11-18
2001-11-27
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S043010, C372S044010, C372S046012, C372S049010, C372S049010, C372S050121
Reexamination Certificate
active
06324199
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to intersubband semiconductor light sources, and, more particularly, to both incoherent, spontaneous emission intersubband sources (akin to LEDs) and coherent, stimulated emission intersubband sources (e.g., lasers).
BACKGROUND OF THE INVENTION
As described by F. Capasso et al. in
Solid State Communications,
Vol. 102, No. 2-3, pp. 231-236 (1997) and by J. Faist et al. in
Science,
Vol. 264, pp. 553-556 (1994), which are incorporated herein by reference, a QC laser is based on intersubband transitions between excited states of coupled quantum wells and on resonant tunneling as the pumping mechanism. Unlike all other semiconductor lasers (e.g., diode lasers), the wavelength of the lasing emission of a QC laser is essentially determined by quantum confinement; i.e., by the thickness of the layers of the active region rather than by the bandgap of the active region material. As such it can be tailored over a very wide range using the same semiconductor material. For example, QC lasers with AlInAs/GaInAs active regions have operated at mid-infrared wavelengths in the 3 to 13 &mgr;m range. In diode lasers, in contrast, the bandgap of the active region is the main factor in determining the lasing wavelength. Thus, to obtain lasing operation at comparable infrared wavelengths the prior art has largely resorted to the more temperature sensitive and more difficult-to-process lead salt materials system.
More specifically, diode lasers, including quantum well lasers, rely on transitions between energy bands in which conduction band electrons and valence band holes, injected into the active region through a forward-biased p-n junction, radiatively recombine across the bandgap. Thus, as noted above, the bandgap essentially determines the lasing wavelength. In contrast, the QC laser relies on only one type of carrier; i.e., it is a unipolar semiconductor laser in which distinct electronic transitions between conduction band states occur; these states arise from size quantization in the active region heterostructure.
The active region of QC lasers includes a multiplicity N (typically ~25) of stacked stages or repeat units, each unit including a radiative transition (RT) region adjacent an injection/relaxation (I/R) region. As the name of the laser implies, electrons cascade from one RT region to the next when a suitable bias voltage is applied across the device. This scheme leads to a slope efficiency (and external differential quantum efficiency) and laser power proportional to N in the linear part of the L-I characteristic, as confirmed by J. Faist et al.,
IEEE J. Quantum Electron.,
Vol. 34, No. 2, pp. 336-343 (Feb. 14, 1998) and C. Gmachl et al.,
Appl. Phys. Lett.,
Vol. 72, No. 24, pp.3130-3132 (Jun. 15, 1998), both of which are incorporated herein by reference. The N stages, which form a common active waveguide core, also increase the optical confinement and, therefore, the modal gain sufficiently to overcome the increased waveguide losses at mid-infrared (e.g., 3-13 &mgr;m) wavelengths, especially when N is large (e.g., ≧10). In fact, early theoretical work of Yee et al.,
Appl. Phys. Lett.,
Vol. 63, No. 8, pp. 1089-1091 (1993) on GaAs/AlGaAs lasers reached the conclusion that a single intersubband transition (in a device having only a single RT region) would not have enough gain in the mid-infrared to reach the lasing threshold. Indeed, the high performance of many QC lasers has heretofore reinforced the notion that a cascaded structure is essential for an intersubband laser.
Thus, a need remains for a unipolar, intersubband semiconductor light source, especially a laser, that is capable of efficient emission at a single intersubband transition in a device having a single RT region.
In addition, the tendency for prior art QC lasers to have a relatively large number of stages (e.g., 25, as noted above) has both processing and operational implications. From a fabrication standpoint a large number of stages means a corresponding large number of relatively thin layers (e.g., 400) have to be epitaxially grown, which in turn requires careful control of the growth process (as to layer thickness, composition and strain compensation). On the other hand, from an operational perspective, a large number of stages typically requires a higher voltage bias (e.g., 6-10 V). Yet, some applications require an optical source which is capable of operation at lower voltages (e.g., <3 V).
Therefore, there is also a need for a unipolar, intersubband semiconductor light source that operates at relatively low voltages.
There is likewise a need for such a light source that has fewer layers and, therefore, is simpler to fabricate.
SUMMARY OF THE INVENTION
In accordance with one aspect of our invention, an intersubband semiconductor light source comprises a core region that includes a unipolar radiative transition (RT) region having upper and lower energy levels, an injector-only (I) region disposed on one side of the RT region, and a reflector/extractor-only (R/E) region disposed on the other side of the RT region. The I region has a first miniband of energy levels aligned so as to inject electrons into the upper energy level, and the R/E region has a second miniband of energy levels aligned so as to extract electrons from the lower energy level. The R/E region also has a minigap aligned so as to inhibit the extraction of electrons from the upper level. A suitable voltage applied across the core region is effective to cause the RT region to generate light at a wavelength determined by the energy difference between the upper and lower energy levels.
Our invention has several advantages. First, by designing the source so that the electron injector and reflector/extractor are located in separate regions, we are able to independently optimize their functions. Second, our invention can be fabricated using many fewer layers than typical QC lasers, which simplifies processing. Third, since our light source is capable of operating with a relatively small number of RT regions, it can also operate at relatively low voltages (e.g., <3 V).
In an alternative embodiment of our invention, the source includes at least two RT regions separated by an injection/relaxation region The I region is disposed adjacent one of the RT regions, and the R/E region is adjacent another of the RT regions. This embodiment also exploits the separate optimization of the I and R/E regions, but in addition contemplates the use of several RT regions to increase the output while retaining the ability to operate at relatively low voltages.
REFERENCES:
patent: 5457709 (1995-10-01), Capasso et al.
patent: 5509025 (1996-04-01), Capasso et al.
patent: 5570386 (1996-10-01), Capasso et al.
patent: 5936989 (1999-08-01), Capasso et al.
patent: 5978397 (1999-11-01), Capasso et al.
Hsu et al.,Intersubband laser design using a quantum box array, SPIE, vol. 3001, pp. 271-281 (1997).
R. F. Kazarinov et al.,Possibility of the Amplification . . ., Soviet Phys.-Semic., vol. 5, No. 4, pp. 707-709 (1971).
W. M. Yee et al.,Carrier transport . . ., Appl. Phys. Lett., vol. 63, No. 8, pp. 1089-1091 (1993).
J. Faist et al.,Phonon limited . . ., Appl. Phys. Lett., vol. 64, No. 7, pp. 872-874 (1994).
J. Faist et al.,Quantum Cascade Laser, Science, vol. 264, pp. 553-556 (1994).
J. Faist et al.,Vertical transition . . ., Appl. Phys. Lett., vol. 66, No. 5, pp. 538-540 (1995).
C. Sirtori et al.,Quantum cascade . . ., Appl. Phys. Lett., vol. 66, No. 24, pp. 3242-3244 (1995).
F. Capasso et al.,Infrared . . ., Solid State Comm., vol. 102, No. 2-3, pp. 231-236 (1997).
G. Scamarcio et al.,High-Power . . ., Science, vol. 276, pp. 773-776 (1997).
J. Faist et al.,High-Power . . ., IEEE J. Quantum Electr., vol. 34, No. 2, pp. 336-343 (Feb. 1998).
J. Faist et al.,Short wavelength . . ., Appl. Phys. Lett., vol. 72, No. 6, pp. 680-682 (Feb. 1998).
Y. B. Li et al.,Mid-infrared . . ., Appl. Phys. Lett., vol. 72, No. 17, pp. 2141-2143 (Apr. 1998).
C. Gmachl et al.,High-power . . ., Appl. Phys. Lett., vol. 72, No. 24, pp. 3
Capasso Federico
Cho Alfred Yi
Chu Sung-Nee George
Gmachl Claire F.
Hutchinson Albert Lee
Arroyo Teresa M.
Jackson Cornelius H.
Lucent Technologies - Inc.
Urbano Michael J.
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