Ballistic transport and surface scattering in (In,Ga)As-InP heterostructure narrow channels

Narrow conduction channels are fabricated from an In0.75Ga0.25As-InP heterostructure using electron-beam lithography and dry etching. The etched surface is realized to be smooth by employing a reactive ion etching. The etching-induced surface conduction is eliminated by removing the damaged surface layer using a diluted HCl solution. The negligible surface depletion for the In-rich quantum well enables to create conducting channels in arbitrary geometries such as in a circular shape. We evidence the presence of a ballistic contribution in the electron transport by demonstrating a rectification of rf excitations that is achieved by the magnetic-field-tuned transmission asymmetry in the circularly-shaped channels. The absence of the surface depletion is shown to cause, on the other hand, a surface scattering for the electrons confined in the channels. An increase of the resistance, including its anomalous enhancement at low temperatures, is induced by the gas molecules attached to the sidewalls of the channels. We also report a large persistent photoconduction, which occurs as a parallel conduction in the undoped InP barrier layer.Peer Reviewe

Two-colour In0.5Ga0.5As quantum dot infrared photodetectors on silicon

An InGaAs quantum dot (QD) photodetector is directly grown on a silicon substrate. GaAs-on-Si virtual substrates with a defect density in the order of 106 cm−2 are fabricated by using strained-layer superlattice as dislocation filters. As a result of the high quality virtual substrate, fabrication of QD layer with good structural properties has been achieved, as evidenced by transmission electron microscopy and x-ray diffraction measurements. The InGaAs QD infrared photodetector is then fabricated on the GaAs-on-Si wafer substrate. Dual-band photoresponse is observed at 80 K with two response peaks around 6 and 15 μm.Engineering and Physical Sciences Research Council https://doi.org/10.13039/501100000266Royal Academy of Engineering https://doi.org/10.13039/501100000287National Science Foundation of the U.S.Peer Reviewe

Photoconductor for emitting and/or receiving electromagnetic waves

The invention relates to a photoconductor for emitting and/or receiving electromagnetic waves, comprising a material region (1) comprising a first and a second section (A, C), wherein the second section (C) provides a higher density of charge carrier trapping centers and/or recombination centers than the first section (A), a confinement generating a sub-band structure of the charge carrier energy states in the material region (1), wherein the first and the second section (A,C) are arranged and configured in such a manner that a maximum of the carrier probability density (P1) of the sub-band ground state is located in one of these sections (A, C) and a maximum of the carrier probability density (P2) of an excited sub-band state is located in the respective other section

Terahertz-Antenne und Verfahren zum Herstellen einer Terahertz-Antenne

The invention relates to a terahertz antenna comprising at least one photoconductive layer (11) which generates charge carriers during the irradiation of light, and two electroconductive antenna elements (21, 22) by which means an electrical voltage can be applied to at least one section of the photoconductive layer (11), the photoconductive layer (11) being doped with a dopant in a concentration of at least 1 x 1018cm-3, the dopant being a transition metal. According to the invention, the photoconductive layer (11) is produced by molecular beam epitaxy at a minimum growth temperature of 200°C and a maximum of 500°C, the dopant being arranged in the photoconductive layer (11) such that it produces a plurality of point defects. The invention also relates to a method for producing a terahertz antenna

Near-infrared intersubband transitions in InGaAs AlAs InAlAs double quantum wells

Intersubband optical transitions at short wavelengths in strain-compensated In0.70Ga0.30As AlAs double quantum wells are investigated by means of mid-infrared absorption. Trade-offs between achieving a high transition energy and a large oscillator strength of the two highest-energy intersubband transitions using our strain-compensation approach are analyzed as a function of the widths of the two wells. Two design strategies leading to relatively strong intersubband optical transitions at 800 meV, 1.55 µm, are described and the corresponding structures grown using gas-source molecular-beam epitaxy on (001)InP are investigated. The strongest intersubband transitions obtained experimentally are generally between 300 and 600 meV, 2 4 µm. Significant oscillator strength, however, also extends out to 800 meV, 1.55 µm

Short-wavelength intersubband absorption in strain compensated InGaAs/AlAs quantum well structures grown on InP

We have studied intersubband absorption in strain compensated InxGa1 xAs/AlAs/InyAl1 yAs multiple quantum wells and superlattices grown on InP. X-ray diffraction shows that the layers are pseudomorphically strained and exhibit slight compositional grading of the interfaces. Owing to the high AlAs barriers, the intersubband absorption can be tailored to wavelengths shorter than 2 µm. In some samples, a small, but non-negligible absorption is also observed with s-polarized light