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Sign-alternating photoconductivity and magnetoresistance oscillations induced by terahertz radiation in HgTe quantum wells
摘要： We report on the observation of terahertz radiation induced photoconductivity and of terahertz analog of the microwave-induced resistance oscillations (MIRO) in HgTe-based quantum well (QW) structures of different width. The MIRO-like effect has been detected in QWs of 20 nm thickness with inverted band structure and a rather low mobility of about 3 × 105 cm2/V s. In a number of other structures with QW widths ranging from 5 to 20 nm and lower mobility we observed an unconventional nonoscillatory photoconductivity signal which changes its sign upon magnetic ?eld increase. This effect was observed in structures characterized by both normal and inverted band ordering, as well as in QWs with critical thickness and linear dispersion. In samples having Hall bar and Corbino geometries an increase of the magnetic ?eld resulted in a single and double change of the sign of the photoresponse, respectively. We show that within the bolometric mechanism of the photoresponse these unusual features imply a nonmonotonic behavior of the transport scattering rate, which should decrease (increase) with temperature for magnetic ?elds below (above) the certain value. This behavior is found to be consistent with the results of dark transport measurements of magnetoresistivity at different sample temperatures. Our experiments demonstrate that photoconductivity is a very sensitive probe of the temperature variations of the transport characteristics, even those that are hardly detectable using standard transport measurements.
关键词： HgTe quantum wells,terahertz radiation,magnetoresistance oscillations,bolometric mechanism,photoconductivity
更新于2025-09-04 15:30:14
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Advantage of heteroepitaxial GaSb thin-film buffer and GaSb dot nucleation layer for GaSb/AlGaSb multiple quantum well structure grown on Si(1?0?0) substrate by molecular beam epitaxy
摘要： We grew a GaSb/Al0.3Ga0.7Sb multiple-quantum-well (MQW) structure on a two-inch Si(1 0 0) substrate using a 100-nm-thick heteroepitaxial GaSb thin-film buffer with a nucleation layer of GaSb dots by molecular beam epitaxy (MBE) and evaluated the surface morphology and the photoluminescence (PL) and X-ray diffraction spectra of the MQW structure. The full width at half maximum of the PL spectrum of the GaSb/Al0.3Ga0.7Sb MQW structure was very narrow, although the buffer thickness was much lower than those for previously reported GaSb-based QW structures on Si(1 0 0) substrates. This indicated that the surface of the 100-nm-thick GaSb thin-film buffer was sufficiently flat to form heterostructures and MQWs. The surface roughness and crystalline quality of the GaSb buffer and MQW structure were strongly dependent on the growth temperature; high-performance devices were realized by optimizing the growth temperature. These results showed the advantage and potential applicability of the GaSb/Al0.3Ga0.7Sb MQW structure and the GaSb thin-film buffer with GaSb dots as a nucleation layer grown on Si(1 0 0) substrates.
关键词： A1. Nucleation layer,B1. Gallium antimonide,A3. Quantum wells,B2. Semiconducting III–V materials,A3. Molecular beam epitaxy (MBE),B1. Silicon substrate
更新于2025-09-04 15:30:14
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Controllable optical bistability and multistability in asymmetric quantum wells via Fano-type interference
摘要： We theoretically investigate the hybrid absorptive-dispersive optical bistability (OB) and optical multistability (OM) behaviors induced by Fano-type interference in a four-subband asymmetric semiconductor double quantum wells (QWs) scheme driven by a degenerate probe field and a coherent coupling field. We show that the appearance or disappearance of OB can be controlled by modulating the strength of the Fano-type interference. We also present the threshold and hysteresis cycle of the OB can be controlled by adjusting the intensity of the coherent coupling field. Moreover, OB can be switched to OM by tuning the frequency detuning of the coherent coupling field or vice versa. This interesting scheme may provide guidance for technological applications in optoelectronics and solid-state quantum information science.
关键词： optical bistability,Fano-type interference,quantum wells
更新于2025-09-04 15:30:14
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Giant Modal Gain Coefficients in Colloidal II-VI Nanoplatelets
摘要： Modal gain coefficient is a key figure of merit for a laser material. Previously, net modal gain coefficients larger than a few thousand cm-1 were achieved in II-VI and III-V semiconductor gain media, but this required operation at cryogenic temperatures. In this work, using pump-fluence-dependent variable-stripe-length measurements, we show that colloidal CdSe nanoplatelets enable giant modal gain coefficients at room temperature, up to 6,600 cm-1 under pulsed optical excitation. Furthermore, we show that exceptional gain performance is common to the family of CdSe nanoplatelets, as shown by examining samples having different vertical thicknesses and lateral areas. Overall, colloidal II-VI nanoplatelets with superior optical gain properties are promising for a broad range of applications, including high speed light amplification and loss compensation in plasmonic photonic circuits.
关键词： colloidal nanoplatelets,optical gain,variable stripe-length method,CdSe,modal gain coefficient,colloidal quantum wells
更新于2025-09-04 15:30:14