Exciton radiative recombination properties of an electronically isolated triple GaAs quantum well (QW) with different thicknesses prepared by growth-interrupted molecular beam epitaxy have been ...investigated with respect to the effect of growth islands present in each QW. When cold excitons with a negligible center-of-mass motion are resonantly photoexcited within each dominant island terrace, the photoluminescence (PL) dynamics of the split exciton lines reflect the exciton intra-well transfer towards the wider-well terraces. However, dramatic changes are observed in both the PL intensity distribution and the dynamics between the QWs as well as between the island terraces under resonant excitation into an excited (
n=2) state of the widest well located just below the barrier band edge. We tentatively attribute the origin of these changes to the different exciton relaxation pathways in terms of center-of-mass kinetic motion of the two-dimensional excitons.
The temperature dependence of the emission properties in a composite quantum well structure consisting of a wide and a narrow GaAs quantum well (QW) separated by and embedded in a GaAs/AlAs ...short-period superlattice (SPS) has been studied by steady-state and time-resolved photoluminescence (PL) measurements. At low temperatures
(20
K)
, distinct PL peaks originating from the QWs and SPS are observed. When the temperature is increased to
60
K
, the PL intensity of the wide QW with strongly confined states significantly increases, while the ones of the narrow QW and the SPS gradually decrease. Above
100
K
, however, the PL intensity of the wide QW decreases and the others increase. The temperature dependence of the PL dynamics indicates that the PL properties of the composite QWs are connected to Bloch-type transport of photoexcited carriers in the SPS between the wide and narrow QW.
We have studied the photoluminescence (PL) properties of a GaAs/Al
x
Ga
1−
x
As quantum well (QW) system containing three QWs with different thicknesses, in which the widest one
(7.8
nm)
has an ...excited-subband exciton state located slightly below the barrier band edge. Using above-barrier excitation with a power density of about
10
W/
cm
2
at
13
K
, a strong PL emission peak appears on the high-energy side of the three PL peaks originating from the ground-state exciton transitions of the three QWs. This high-energy PL peak with an intensity comparable to the one of the other three peaks is located near an excited-subband (
n=2) exciton state of the widest QW. By investigating the position dependence of the PL spectra across a 2-inch wafer, which exhibits a decreasing Al mole fraction
x from the center to the edge, the PL intensity of the high-energy peak can be correlated with the one of the ground state in the widest QW. This correlation indicates that this high-energy PL peak is most likely related to the
n=2 exciton state of the widest QW because of the energy alignment of the excited subband state relative to the barrier band edge.
We report on a compact terahertz (THz) source based on a quantum-cascade laser (QCL). The source is intended for a local oscillator in a THz heterodyne receiver for the detection of the fine ...structure line of neutral atomic oxygen (OI) at 4.7448 THz. The QCL, which is mounted in a small mechanical cryocooler, employs a GaAs/AlAs active region heterostructure and a resonator with an additional back-facet mirror. This allows for low electrical pump powers of less than 1.2 W and high output powers of up to 8 mW. The whole setup weighs less than 4 kg. The application of such a system in a spaceborne mission appears to be feasible.
Summary form only given. The design and the performance of a 4.7-THz local oscillator (LO) for the GREAT (German REceiver for Astronomy at Terahertz frequencies) heterodyne spectrometer on SOFIA, the ...Stratospheric Observatory for Infrared Astronomy, are presented. The LO is based on a quantum-cascade laser, which is mounted in a compact mechanical cryocooler. It delivers up to 150 μW output power into a nearly Gaussian shaped beam around the frequency of the fine structure line of neutral atomic oxygen, OI, at 4.7448 THz.
We report on the development of a 4.7-THz local oscillator (LO) for the heterodyne spectrometer GREAT on SOFIA. The design of the LO and its performance in terms of output power, frequency accuracy, ...frequency stability, and beam profile as well as its implementation in GREAT will be presented.
