Recent improvements in quantum cascade laser technology have led to a number of very impressive results. This paper is a brief summary of the technological development and state-of- the-art performance of quantum cascade lasers produced at the Center for Quantum Devices. Laser design will be discussed, as well as experimental details of device fabrication. Room temperature QCL operation has been reported for lasers emitting between 5 - 11 micrometers , with 9 - 11 micrometers lasers operating up to 425 K. We also demonstrate record room temperature peak output powers at 9 and 11 micrometers (2.5 W and 1 W respectively) as well as record low 80 K threshold current densities (250 A/cm<SUP>2</SUP>) for some laser designs. Finally, some of the current limitations to laser efficiency are mentioned, as well as a means to combat them.
We have studied the dependence of the well doping density in n-type GaInAs/InP quantum well IR photodetectors (QWIPs) grown by low-pressure metalorganic chemical vapor deposition. Three identical GaInAs/InP QWIP structures were grown with well sheet carrier densities of 1 by 10<SUP>11</SUP> cm<SUP>-2</SUP>, 3 by 10<SUP>11</SUP> cm<SUP>-2</SUP>, and 10 by 10<SUP>11</SUP> cm<SUP>-2</SUP>; all three samples had very sharp spectral response at (lambda) equals 9.0 micrometers . We find that there is a large sensitivity of responsivity, dark current, noise current, and detectivity with the well doping density. Measurements revealed that the lowest-doped samples had an extremely low responsivity relative to the doping concentration while the highest-doped sample had an excessively high dark current relative to doping. The middle-doped sample yielded the optimal results. This QWIP had a responsivity of 33.2 A/W and operated with a detectivity of 3.5 by 10<SUP>10</SUP> cmHz<SUP>1/2</SUP>W<SUP>-1</SUP> at a bias of 0.75 V and temperature of 80 K. This responsivity is the highest value reported for any QWIP in the (lambda) equals 8-9 micrometers range. Analysis is also presented explaining the dependence of the measured QWIP parameters to well doping density.
Multi-quantum well structures of Ga<SUB>x</SUB>In<SUB>1-x</SUB>As<SUB>y</SUB>P<SUB>1-y</SUB> were grown by metalorganic chemical vapor deposition for the fabrication of quantum well IR photodetectors. The thickness and composition of the wells was determined by high-resolution x-ray diffraction and photoluminescence experiments. The intersubband absorption spectrum of the Ga<SUB>0.47</SUB>In<SUB>0.53</SUB>As/InP, Ga<SUB>0.38</SUB>In<SUB>0.62</SUB>As<SUB>0.80</SUB>P<SUB>0.20</SUB> (1.55 micrometers )/InP, and Ga<SUB>0.27</SUB>In<SUB>0.73</SUB>As<SUB>0.57</SUB>P<SUB>0.43</SUB> (1.3 micrometers )/InP quantum wells are found to have cutoff wavelengths of 9.3 micrometers , 10.7 micrometers , and 14.2 micrometers respectively. These wavelengths are consistent with a conduction band offset to bandgap ratio of approximately 0.32. Facet coupled illumination responsivity and detectivity are reported for each composition.