I. Hase

Current-voltage characteristics through GaAs/AlGaAs/GaAs heterobarriers grown by metalorganic chemical vapor deposition

Current–voltage characteristics of GaAs/AlxGa1−xAs /GaAs heterobarriers grown by metalorganic chemical vapor deposition were investigated for x from 0.32 to 0.46. Calculation of the current, which included just two components—a tunneling component and a thermionic component—agreed well with experimental results. The tunneling effective mass used is the same as the Γ point effective mass when x is 0.32; this value allows the calculated results to fit the experimental data. The tunneling effective mass becomes much larger than the Γ point mass as x increases. This fact suggests that the other band edge X participates in the tunneling process, making the effective mass larger as it approaches the Γ point edge. The barrier heights deduced from I–V and I–T relations are in good agreement. The results support a ratio of 60%–65% of AlGaAs/GaAs conduction‐band discontinuity to the total band‐gap difference.

Tunneling Spectroscopy of InAs Wetting Layers and Self-Assembled Quantum Dots: Resonant Tunneling through Two- and Zero-Dimensional Electronic States.

Using GaAs/AlGaAs/InAs/AlGaAs/GaAs tunneling diodes, we have investigated the resonant tunneling current through InAs wetting layers and self-assembled quantum dots obtained from the Stranski-Krastanow growth mode. For InAs layers both with and without the quantum dots, resonant tunneling current through two-dimensional (2D) electronic states in the wetting layers is observed. From this observation, we can determine the 2D ground state energy. On the other hand, current peaks due to resonant tunneling from three-dimensional (3D) electronic states in the emitter to zero-dimensional (0D) states in the quantum dots are observed only for the case of an InAs layer with the quantum dots.

Single electron–photon logic device using coupled quantum dots: Computation with the Fock ground state

We propose a novel logic device using coupled quantum dots (CQDs) in which single‐electron tunneling is influenced by electron–electron interaction. If occupation/unoccupation by a single electron in a quantum dot is viewed as a bit 1/0, we can say that the device can perform (N)AND and (N)OR operations simultaneously. Data input/output is performed by irradiation/absorption of photons. The (N)AND and (N)OR operations are performed by the relaxation of the electronic system to the (Fock) ground state which depends on the number of electrons in CQDs. When the device is constructed of semiconductor nanostructures, phonon emission from an electron is the main contributor to the energy dissipation process. We also present results of a theoretical analysis of the device performance. These results show that (i) the error probability at the final state depends on only the dissipation energy and becomes smaller as the dissipation energy becomes larger, and (ii) the speed of operation depends on the dissipation en...

Noninteger InAs monolayer well InAs/GaAs single quantum well structures grown by metalorganic chemical vapor deposition

InAs/GaAs single quantum well structures have been grown by metalorganic chemical vapor deposition. The grown wells are 1.03, 1.3, and 1.7 InAs monolayers thick. The 4 K photoluminescence spectra exhibit strong and narrow peaks, their energy decreasing smoothly with increasing well thickness. The noninteger value is interpreted on the model that the interface is macroscopically flat but has valleys and hills with their lateral extent smaller than excitons. The effective interface position is determined by their relative lateral extent.

Diameter dependence of current–voltage characteristics of ultrasmall area AlSb–InAs resonant tunneling diodes with diameters down to 20 nm

We have studied the current–voltage characteristics I(V) of ultrasmall area AlSb–InAs resonant tunneling diodes (RTDs) with diameters down to 20 nm. Resonant tunneling peaks were observed for all the diodes at room temperature. The peak-to-valley ratio reduces with the decreasing diameter of the RTD. We found from the diameter dependence of the valley current that the reduction is due to a contribution of the thermally activated surface current to the valley current. For RTDs with diameters less than 100 nm, we observed fine structures around zero bias at 4 K. They can be attributed to tunneling through zero-dimensional states confined by a RTD sidewall.

AlGaAs/GaAs quantum structures grown by MOCVD — Coupled quantum well photoluminescence and vertical transport through hetero-barriers

Abstract A quantum-mechanically coupled well system consisting of two GaAs wells 30 A thick separated by a 20 A thick Al0.5Ga0.5As layer has been grown by MOCVD. The photoluminescence spectra of this system show the splitting of degenerate single well states into doublet states, i.e. a symmetric state and an antisymmetric state. Good agreement between theoretical and experimental transition energies was obtained. Only quantum-well luminescence was observed, indicating that there was no alloy clustering in the 20 A thick AlGaAs barrier. Vertical transport diodes consisting of a 200 A thick AlxGa1-xAs (x=0.4, 0.7) barrier layer sandwiched betwe en n+-GaAs have been fabricated. Current-voltage characteristics and temperature dependence of the current are well derived as a sum of the tunneling current and the thermionic emission current through a AlGaAs barrier with a reasonable barrier height.

Electron correlations in coupled quantum dots

The quantum states of two electrons in a pair of coupled quantum dots confined by heterostructures of compound semiconductors were calculated. As the physical parameters were changed various quantum states of electrons were obtained. The correlation between electrons in these quantum states is analyzed using the mean distance between electrons and its variance. When the quantum states include quadruple degenerate ground states, electrons are localized on each quantum dot and all kinetic movement except spin is frozen. This suggests that a Mott insulator phase will appear in a bulk array of coupled quantum dots. Because coupled quantum dot arrays can be assembled to include both metallic regions and insulating regions without changing the density of electrons, they have great potential in applications for future electron devices.

InAs-GaSb hot electron transistors grown by metalorganic chemical vapor deposition

Abstract We report on GaSb and GaInSb epilayers grown on GaSb substrates by LPMOCVD. Growth was performed at 100 Torr from TMGa, TMIn, and TMSb. The growth rate using TMGa is reduced at lower temperatures. This determines x in Ga 1− x In x Sb. The growth efficiency is also reduced by adding TMSb to the vapor. A hot-electron transistor structure was also grown. The device uses a GaSb emitter barrier and 100Awide InAs base. A GaSb collector barrier and a Ga 0.9 In 0.1 Sb(200A)/GaSb collector barrier were used. The latter device exhibits a common-emitter current gain in excess of 1 at room temperature.

Intervalley scattering observed in an AlGaAs/GaAs hot‐electron transistor

Electron transfer into the L and X bands of GaAs is observed in the dependence of transfer ratio α (collector current Ic/emitter current Ie) of an AlGaAs/GaAs hot‐electron transistor upon emitter‐base voltage Veb. The α‐Veb curve and its variation with temperature change confirms the idea that electron transfer to the higher bands randomizes the electron motion and is effective in reducing α. The differential transfer ratio Δα (dIc/dIe) shows double peaks and a clear shoulder. The lower‐energy peak may indicate the onset of elastic intervalley scattering.

Tunneling current through self-assembled InAs quantum dots embedded in symmetric and asymmetric AlGaAs barriers

Abstract In order to study tunnelling current through individual self-assembled quantum dots, we have fabricated tunnel diodes with a small number of self-assembled InAs quantum dots embedded in symmetric and asymmetric AlGaAs barriers. In the current–voltage characteristics of the symmetric barrier diode, we have observed current peaks due to resonant tunneling through zero-dimensional states in the individual quantum dots for both voltage polarities. In contrast, we have found that the behavior of the asymmetric barrier diodes depends on the voltage polarity. For the voltage polarity such that the electrons enter the quantum dots through the thick barrier and leave through the thin one, the zero-dimensional resonant tunneling current peaks are observed as in the symmetric barrier case. On the other hand, in the opposite voltage polarity, such that collector barrier is less transparent, current step structures are observed. The step structures are attributed to Coulomb staircase due to enhanced electron accumulation in the quantum dots. Assuming a double tunnel capacitor model, the size of the conducting channel deduced from the step-width of the staircase is in agreement with the lateral size of one quantum dot obtained by atomic force microscope measurements.