Electron Tunneling in Superlattices with Distributed THz Cavities
I.V. Altukhov1, M.S. Kagan1, S.K. Paprotskiy1, A.N. Baranov2, R. Teissier2, A.D. Buravlev3, N.D. Il’inskaya3, Yu.M. Zadiranov3, A.A. Usikova3,
A.P. Vasil’iev3, V.M. Ustinov3
1V.A. Kotel’nikov Institute of Radio Engineering and Electronics,
Russian Ac. Sci., Moscow
2IES, Université Montpellier 2, CNRS, Montpellier, France
3A.F. Ioffe Physico-Technical Institute, Russian Ac. Sci., St. Petersburg
The main problem in the development of tunable semiconductor THz sources suitable for practical use is the possibility tooperate in continuous-wave regime at room temperature. Note, that the semiconductor THz lasers operate at cryogenic temperatures only and can not work at room temperature (kT=25 meV) because the energies of quanta in THz range are around 10 meV and to obtain the population inversion at room T is practically impossible. So, we need to reject the laser scheme and to look for another way to get THz generation at room T. The reasonable idea seems to look for a semiconductor system with a fast negative differential conductivity (NDC), which can produce THz oscillations in a suitable resonant cavity.Superlattices are promising for THz emission to realize as the relaxation times of conductivity and space charge in the SLs can correspond to the THz range.
The studies of the effect of distributed terahertz (THz) cavity on the tunneling current in superlattices (SL) InAs/AlSb and GaAs/AlAs at room temperature are presented. The SLs consisted of 60 and 100 periods, respectively, were sandwiched between heavily doped cap layer and the substrate. Metallic contacts to the produced mesa structures had the form of a ring and formed a distributed cavity for free-space wavelengths of 110 to 160 μm.
Several equidistant maxima were observed on current-voltage characteristics in the range of non-resonant tunneling (at voltages, when the overlapping of ground confined states in the neighboring quantum wells and corresponding miniband transport disappear). Voltage differences between the maxima were correlated to the resonant frequency of the cavity. The origin of these maxima is attributed to the Purcell effect that is the enhancement of spontaneous electromagnetic emission into the cavity as compared with the emission into free space.
The vertical transport in the short-period GaAs/AlAs SLs was studied in the region of miniband conductivity (at the presence of electric domains). The electric domain formation at a threshold voltage was accompanied by steep current drop. The current jump could reach 50%. It has been found that this threshold voltage changes considerably under the variation of the cavity parameters. The shift of the threshold has been explained by the excitation of high-amplitude oscillations in the cavity. Indeed, if an ac voltage of comparable amplitude is applied to the sample with a nonlinear current–voltage characteristic in addition to the dc voltage, an additional dc voltage appears because of the detection and shifts the operating point. Thus, this experiment indicates the excitation of THz oscillations in the cavity owing to the negative resistance of the superlattice with domains.
This work was supported by the Russian Foundation for Basic Research (grants 14-02-01062 and 16-29-03135) and RAS programs “Basic research on nanotechnology and nanomaterials” and “Modern problems of radiophysics”.