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Register a new userInfrared detector based on conduction band intersubband transitions in a heterojunction between two quantum wires
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In this paper we study the feasibility of an infrared detector based on intersubband transitions in the conduction band of the junction between two semiconductor quantum wires. We show that by varying the radius of the wires it is possible to engineer a band structure of the junction that would be favorable for creating and detecting photocurrent. The suggested concept also allows for broadband detection based on arrays of wires with different radii.
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: n-type Ge/SiGe asymmetric-coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through the comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune by design the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are the promising starting point towards a working electrically pumped light-emitting device.
We study the conductance threshold of clean nearly straight quantum wires in which an electron is bound. We show that such a system exhibits spin-dependent conductance structures on the rising edge to the first conductance plateau, one near 0.25(2e^2/h), related to a singlet resonance, and one near 0.75(2e^2/h), related to a triplet resonance. As a quantitative example we solve exactly the scattering problem for two-electrons in a wire with circular cross-section and a weak bulge. From the scattering matrix we determine conductance via the Landauer-Buettiker formalism. The conductance anomalies are robust and survive to temperatures of a few degrees. With increasing magnetic field the conductance exhibits a plateau at e^2/h, consistent with recent experiments.
Temperature dependence of intersubband transitions in AlN/GaN multiple quantum wells grown with molecular beam epitaxy is investigated both by absorption studies at different temperatures and modeling of conduction-band electrons. For the absorption study, the sample is heated in increments up to $400^circ$C. The self-consistent Schrodinger-Poisson modeling includes temperature effects of the band-gap and the influence of thermal expansion on the piezoelectric field. We find that the intersubband absorption energy decreases only by $sim 6$ meV at $400^circ$C relative to its room temperature value.
We have calculated the contribution of intersubband transitions to the third order optical nonlinear susceptibility, $chi^{(3)}(omega,omega,omega)$ for nonresonant as well as resonant third harmonic generation and $chi^{(3)}(omega,-omega,omega)$ for nonlinear refraction and absorption. As examples, we consider InAs/AlSb and GaAs/GaAlAs quantum wells. The effects of finite barrier height, energy band nonparabolicity, and high carrier concentrations are included. It is shown that quantum confinement, rather than the band nonparabolicity, is responsible for high values of nonresonant $chi^{(3)}_{zzzz}$. Very high values of $chi^{(3)}_{zzzz}$ are obtained for third harmonic generation and two photon absorption for incident wavelength near 10.6 $mu$m. Intensity dependence of refractive index and of absorption co-efficient is also discussed for intensity well above the saturation intensity. Effective medium theory is used to incorporate the collective effects.
We examine theoretically the intersubband transitions induced by laser beams of light with orbital angular momentum (twisted light) in semiconductor quantum wells at normal incidence. These transitions become possible in the absence of gratings thanks to the fact that collimated laser beams present a component of the lights electric field in the propagation direction. We derive the matrix elements of the light-matter interaction for a Bessel-type twisted-light beam represented by its vector potential in the paraxial approximation. Then, we consider the dynamics of photo-excited electrons making intersubband transitions between the first and second subbands of a standard semiconductor quantum well. Finally, we analyze the light-matter matrix elements in order to evaluate which transitions are more favorable for given orbital angular momentum of the light beam in the case of small semiconductor structures.
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