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(Color online) (a) Self-consistent solution of coupled Schrödinger and Poisson equations for an applied electric field of for N892. The nominal layer sequence, starting from the injection barrier is (in nm): . barriers are represented by bold face numbers and the underlined layer is doped with Si, in density. The doping level yields a nominal sheet carrier density of and an average doping density of . (b) Measured and simulated x-ray diffraction of the grown structure (N892).
(Color online) (a) Pulsed and (b) cw characteristics of a long and wide sample of the structure N892. The inset shows the voltage-current characteristic and differential resistance at . For the power measurement an absolute terahertz power meter was used (Thomas Keating Instruments). In pulsed mode operation the device was biased with pulse trains of repeated at , modulated by a square wave, giving an effective duty cycle of 5%. For cw measurements a mechanical chopper at was used. The light is collected and guided to the power meter with a straight cone.
(Color online) (a) Pulsed and (b) cw characteristics of a long and wide sample of the structure N908. The inset shows the voltage-current characteristic and differential resistance at . The same power measurement setup as described in the caption of Fig. 2 was used.
(Color online) (a) Spectral characterization in the cw mode at of two devices; one from the structure N892 and the other from N908. Both samples are long and wide. (b) Comparison of the differential resistance in the cw mode at between the devices of Fig. 2 and 3. (c) Threshold current density versus temperature in pulsed mode of the devices of Fig. 2 and 3. The solid lines are guides for the eye. The devices were operated at a very low duty cycle (0.12%) and the lasing threshold was detected with a bolometer.
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