K. P. Martin

Bias circuit effects on the current‐voltage characteristic of double‐barrier tunneling structures: Experimental and theoretical results

Using the stable, dc current‐voltage (I‐V) curve measured from a double‐barrier resonant tunneling structure, we have studied the effects of external circuit elements on device oscillations. A simulation, using the experimental I‐V and a simple circuit model for the biasing arrangement, showed that hysteresis and vertical jumps appear in the current‐voltage curve when the circuit oscillates. This observation is supported by experimental results obtained on the same device with external circuit elements intentionally added to the biasing configuration.

Transverse magnetic field dependence of the current-voltage characteristics of double-barrier quantum well tunneling structures

We report the effects of a transverse magnetic field (J⊥B) on the conductivity of quantum well tunneling structures based on AlGaAs/GaAs/AlGaAs quantum wells. The current‐voltage characteristics in the positive differential resistance regime show negative magnetoconductance for all values of B. The peak bias voltage increases monotonically with increasing B. For B 6 T. The data also show dramatic magnetic field induced changes in the negative differential resistance (NDR) features. The behavior of the NDR changes from sharp hysteretic bistable‐like transitions to astable NDR transitions. Both the valley current and its bias voltage position increase with increasing magnetic field. This behavior is described by a simple model that includes magnetic field effects across the barriers.

Experimental investigation of the ratchet effect in a two-dimensional electron system with broken spatial inversion symmetry

We report on experimental evidence of directed electron transport, induced by external linear-polarized microwave irradiation, in a two-dimensional spatially-periodic asymmetrical system called ratchet. The broken spatial symmetry was introduced in a high mobility two-dimensional electron gas based on AlGaAs/GaAs heterojunction, by patterning an array of artificial semi-discs-shaped antidots. We show that the direction of the transport is efficiently changed by microwave polarization. The dependence of the effect on magnetic field and temperature is investigated. This represents a significant step towards the realization of new microwave detectors and current generators.

Influence of ballistic electrons on the device characteristics of vertically integrated resonant tunneling diodes

We present a systematic study of the ballistic electron contribution to the current‐voltage (I‐V) characteristics of vertically integrated resonant tunneling diodes (RTDs) separated by doped spacer layers (Wsp). A magnetic field (B) transverse to the tunneling direction was used to tune the electron’s longitudinal energy. The results confirm the isolated circuit element picture of the Wsp=1000 A sample and the strongly coupled description of the 0 A sample. This work shows that even for some nominally isolated RTDs (in this work for Wsp= 400 and 500 A), the I‐V characteristics can undergo striking B‐induced changes. This effect is due to resonant charge buildup in the well of the collector RTD from the relatively weak ballistic component of the current traversing the doped spacer region. A simple model that includes a calculation of the conduction‐band profile and quantum well energy levels under bias gives good agreement with the data.

Magnetotransport studies of charge accumulation in an AlInAs/GaInAs tunneling structure

We report a study of the current‐voltage characteristics of a double barrier, lattice matched, quantum well tunneling structure in a quantizing magnetic field (B∥J). Experiments were conducted at fields up to 23 T at 1.5 K. The heterostructure investigated had 400 A spacer layers in the emitter and collector, a barrier width of 72 A, and a 43‐A‐wide quantum well. This structure showed one negative differential resistance region with a peak‐to‐valley ratio of 23 at 4.2 K. We observed magnetoquantum oscillations, periodic in 1/B, associated with tunneling from a quantized state in the emitter. The overall magnetoconductance dramatically changed with applied bias. We associated these variations with a field‐induced increase of the impedance of the undoped spacer layers. The frequency of these oscillations increased linearly with applied bias. A discontinuity in this dependence is observed around the peak bias voltage which is the direct result of the dynamical storage and release of charge in the well.

Gamma -X intervalley tunnelling in a GaAs/AlAs resonant tunnelling diode under uniaxial stress

Longitudinal uniaxial stress (O<S<36 kbar) at 300 K and 77 K was used to experimentally examine intervalley tunnelling processes in a GaAs/AlAs resonant tunnelling diode (RTD) by lowering quasibound states confined in AlAs X-point quantum wells with respect to the Gamma -point conduction band profile. Intervalley resonances were observed that arose from tunnelling through: (i) large effective mass longitudinal X-states, (ii) a small-mass transverse X-state, and (iii) longitudinal X-states in AlAs aligned with the Gamma -point ground state confined in the adjacent GaAs quantum well, resulting in a resonance with a bias voltage position that increased (decreased) with increasing stress for X-states in the emitter (collector) AlAs layer. At 77 K, intervalley tunnelling can provide resonances of magnitude comparable with the intravalley Gamma resonance. Intervalley resonances remained observable in the differential conductance at 300 K. Self-consistent calculations of device characteristics agreed with the data and established voltage-stress domains for all possible intervalley resonances in the RTD.

Observation of resonant tunneling through localized continuum states in electron wave interference diodes

A 13 layer aperiodic semiconductor superlattice electron wave interference filter, designed with thin‐film optical interference filter techniques by using the analogies between electromagnetic wave propagation in dielectrics and ballistic electron wave propagation in semiconductors, was realized in the GaAs/AlGaAs material system. Current‐voltage measurements at 300 and 77 K show negative differential resistance peaks (with peak‐to‐valley current ratios of 1.25 and 3.9, respectively) that represent observation of tunneling through an above barrier localized quasibound state. We show that electron wave interference devices could compete with resonant tunneling diodes as high frequency oscillators based on dc device characteristics and theoretical subpicosecond tunneling traversal times.

Ballistic Electron Contributions in Vertically Integrated Resonant Tunneling Diodes

Abstract We present a systematic study of the ballistic electron contribution to the current-voltage (I–V) characteristics of vertically integrated resonant tunneling diodes (RTDs). The doped spacer layer separating the two RTDs was varied from 0 to 1000 A. The conduction band profile and quantum well energy levels were determined from a self-consistent model as a function of bias voltage. A magnetic field transverse to the tunneling direction was used to tune the electrons longitudinal energy. The results confirm the isolated RTD picture of the 1000 and 500 A spacer samples, and the strongly coupled description of the 0 A sample. The data also show that under certain circumstances, even for isolated RTDs, the overall I–V characteristics can be very sensitive to resonant charge buildup from a weak ballistic component of the current. We observed Γ - X interband tunneling contributions by ballistic electrons with high kinetic energies.