Quasi-one-dimensional transport characteristics of ridge-type InGaAs quantum-wire field-effect transistors

Abstract

Ridge-type InGaAs/InAlAs quantum-wire field-effect transistors are realized by selective molecular-beam epitaxy and their transport characteristics are studied. An analysis of the depopulation of one-dimensional subbands in these structures reveals little evidence for sidewall depletion, and yields an estimate for the carrier density in good agreement with that found in two-dimensional InGaAs/InAlAs heterojunctions. Subband splittings as large as 7.4 meV are obtained in the wires, indicating their excellent one-dimensional transport properties.

Quantum-interference characteristics of a 25 nm trench-type InGaAs/InAlAs quantum-wire field-effect transistor

“…In previous studies of much wider ridge-type QWR-FETs, we exploited the observation of onedimensional subband depopulation to determine the carrier density and effective width of the wires, and this revealed their excellent one-dimensional characteristics. 16 In our studies here, however, no evidence of Shubnikov-de Haas behavior is seen in the magnetoresistance, which is actually consistent with transport being dominated by the ultranarrow wire. For carrier density typical of ridge-type QWRs (3 ϫ10 12 cm Ϫ2 ), 16 we calculate that a magnetic field larger than 20 T would be required in order for the cyclotron orbit to fit within the trench-wire width of 25 nm.…”

“…16 In our studies here, however, no evidence of Shubnikov-de Haas behavior is seen in the magnetoresistance, which is actually consistent with transport being dominated by the ultranarrow wire. For carrier density typical of ridge-type QWRs (3 ϫ10 12 cm Ϫ2 ), 16 we calculate that a magnetic field larger than 20 T would be required in order for the cyclotron orbit to fit within the trench-wire width of 25 nm. ͑In our cryostat, the maximum magnetic field available is 8 T, at which limiting value evidence of Landau-level condensation is not found in the magnetoresistance͒.…”

“…The origin of this strong enhancement remains undetermined, but is supported by the observations here. Qualitatively, at least, we recall that in our recent study of ridge-type InGaAs QWRs, 16 we found evidence of strongly enhanced subband splitting, which appears to be associated with the smaller effective mass of the electron in InGaAs (m*ϭ0.04 m 0 ), compared to that for GaAs (m*ϭ0.067 m 0 ). In the presence of this enhanced onedimensional level separation, it seems plausible to assume that the intersubband scattering rate should be strongly suppressed, which in turn could lead to the high degree of phase coherence exhibited by this QWR structure.…”

“…[1][2][3][4][5][6][7][8][9] In spite of progress in the techniques of facet-selective molecular-beam epitaxy ͑MBE͒ 1-6 and in situ cleaved-edge overgrowth, [7][8][9] however, relatively few studies to date have focused on the electrical properties of QWRs realized by these approaches. 5,[10][11][12][13][14][15][16] In this letter, we therefore discuss the results of studies of the quantum-interference characteristics of a 25 nm, trench-type InGaAs/InAlAs quantum-wire field-effect transistor ͑QWR-FET͒ realized by selective epitaxy on a patterned InP substrate. The lowtemperature magnetoresistance of the FET is found to exhibit reproducible fluctuations, indicating the importance for transport of electron interference.…”

“…1, in which additional ␦-doped layers facilitate the formation of nonalloyed ohmic contacts to the QWR.͒ After etching away the sidewalls, leaving just a single wire, the etched surface was passivated by depositing a 100 nm SiO 2 film, into which windows were opened and Ti/Au evaporated to form nonalloyed source and drain contacts with lateral separation of 4 m. As the final processing step, a Pt/Ti/Au Schottky gate 2 m in length was deposited between the source and drain using recess etching and liftoff. 15,16 The finished device was then mounted on a standard chip holder, and cooled in the dark in thermal contact with the mixing chamber of a dilution refrigerator. Its magnetoresistance was measured at temperatures in the range of 0.01-10 K, using small constant currents and audio-frequency lock-in detection to avoid unwanted heating electrons.…”