http://dspace-roma3.caspur.it:80 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. 2013-06-20T09:43:36Z http://hdl.handle.net/2307/336 <Title>Study of the Coupling of Terahertz Radiation to HeterostructureTransistors with a Free Electron Laser Source</Title> <Authors>Ortolani, Michele; Di Gaspare, Alessandra; Giovine, Ennio; Evangelisti, Florestano; Foglietti, Vittorio; Doria, Andrea; Gallerano, Gian Piero; Giovenale, Emilio; Messina, Giovanni; Spassovsky, Ivan; Lanzieri, Claudio; Peroni, Marco; Cetronio, Antonio</Authors> <Issue Date>2009-12</Issue Date> <Is part of>Journal of Infrared, Millimeter, and Terahertz Waves</Is part of> <Volume>30</Volume> <Pages>1362-1373</Pages> <Abstract>High electron mobility transistors can work as room-temperature directdetectors of radiation at frequency much higher than their cutofffrequency. Here, we present a tool based on a Free Electron Lasersource to study the detection mechanism and the coupling of the highfrequency signal into the transistor channel. We performed a mappingover a wide area of the coupling of 0.15 THz radiation to an AlGaN/GaNtransistors with cut-off frequency of 30 GHz. Local,polarization-dependent irradiation allowed us to selectively couple thesignal to the channel either directly or through individual transistorbias lines, in order to study the nonlinear properties of thetransistor channel. Our results indicate that HEMT technology can beused to design a millimeter-wave focal plane array with integratedplanar antennas and readout electronics.</Abstract> 2009-11-30T23:00:00Z http://hdl.handle.net/2307/317 <Title>Terahertz intersubband absorption and conduction band alignment inn-type Si/SiGe multiple quantum wells</Title> <Authors>Ciasca, Gabriele; De Seta, Monica; Capellini, Giovanni; Evangelisti, Florestano; Ortolani, Michele; Virgilio, Michele; Grosso, Giuseppe; Nucara, Alessandro; Calvani, Paolo</Authors> <Issue Date>2009</Issue Date> <Is part of>Phisical review B</Is part of> <Volume>79</Volume> <Pages>085302</Pages> <Abstract>Absorption due to conduction intersubband transitions is studied inn-type s-Si/SiGe multiquantum wells (MQW) of different well widths andbarrier composition grown by UHV-chemical vapor deposition (CVD). Themeasured intersubband transition energies are compared with thetheoretical results of a tight-binding model which provides theelectronic band structure of the complete MQW system throughout thewhole Brillouin zone. Our findings demonstrate both the high quality ofthe CVD grown MQWs and the effectiveness of the adopted tight-bindingmodel in describing band profiles and electronic structures of SiGemultilayer systems. In particular we have evaluated the conduction bandoffsets in the investigated structures.</Abstract> 2008-12-31T23:00:00Z http://hdl.handle.net/2307/314 <Title>Conduction band intersubband transitions in Ge/SiGe quantum wells</Title> <Authors>De Seta, Monica; Capellini, Giovanni; Busby, Yan; Evangelisti, Florestano; Ortolani, Michele; Virgilio, Michele; Grosso, Giuseppe; Pizzi, Giovanni; Nucara, Alessandro; Lupi, Stefano</Authors> <Issue Date>2009-08</Issue Date> <Is part of>Applied Physics Letters</Is part of> <Volume>95</Volume> <Pages>051918-051918-3</Pages> <Abstract>In this letter we present the experimental evidence of intersubbandabsorption in the conduction band of compressively strained germaniumquantum wells bounded by Ge-rich SiGe barriers. The measured absorptionenergies are in the terahertz range and are interpreted by means oftight binding calculations which include self-consistent band-bendingand depolarization effects. From the comparison of experimental andnumerical results a conduction band offset along the L line of about120 meV has been estimated for the studied heterostructures.</Abstract> 2009-07-31T22:00:00Z