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Two-well terahertz quantum-cascade laser with direct intrawell-phonon depopulation
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10.1063/1.3243459
/content/aip/journal/apl/95/14/10.1063/1.3243459
http://aip.metastore.ingenta.com/content/aip/journal/apl/95/14/10.1063/1.3243459
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Conduction band diagram of the two-well (three-level) QCL design implemented in . Electrons are injected into the upper laser level 3 from the injector by resonant-tunneling. The optical gain is due to the photon-assisted tunneling transition (Ref 7). The depopulation of the lower laser level 2 occurs directly by fast intrawell electron-longitudinal-optical (e-LO) phonon scattering back into the injector level 1 where . The layer thicknesses starting from the injector barrier in nm are 5.6/7.1/3.1/16.7. The injector well is uniformly -doped to obtain an effective 2D density of per period. At the design bias (17 kV/cm), and (4.6 THz).

Image of FIG. 2.
FIG. 2.

Pulsed (100 ns pulses repeated at 10 kHz) characteristics from a ridge laser. The top inset shows the variation of threshold current density vs the heat-sink temperature . The bottom inset shows representative spectra measured at 10 K.

Image of FIG. 3.
FIG. 3.

(a) cw and measurements vs heat-sink temperature for a ridge laser. The initial discontinuity in the curves marks the onset of lasing. Values of and were measured for this device suggesting a differential of between the heat-sink temperature and the lattice temperature. The inset shows temperature variation of the fractional discontinuity in at threshold for the same device. is the value of just below threshold and is taken as the value of occurring immediately after a smaller second discontinuity that happens at . Temperature variation of the peak current-density , which is characterized by the discontinuity in the at that occurs due to level misalignment beyond the resonance, is also shown. (b) cw for the same device (measured similarly as in Ref. 15). 10 K spectra at different points in the corresponding are also shown. Every change in the lasing optical mode is accompanied by a change in the slope of the (due to the changing beam shape), and also triggers a corresponding occurrence of a smaller discontinuity in the beyond the initial one. While the lasing mode changes with bias due to a Stark shifted gain spectrum, the reason for the corresponding (much smaller) change in the are not yet clear. Also note that the last discontinuity at is not due to light turning off unlike that observed in Ref. 13. The upper inset shows calculated value of due to LO phonon scattering, where an electronic temperature of 200 K is assumed for the upper level population.

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/content/aip/journal/apl/95/14/10.1063/1.3243459
2009-10-08
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Two-well terahertz quantum-cascade laser with direct intrawell-phonon depopulation
http://aip.metastore.ingenta.com/content/aip/journal/apl/95/14/10.1063/1.3243459
10.1063/1.3243459
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