Formation Of Electric Field Domains Research Articles

Strong impact of impurity bands on domain formation in superlattices

The formation of electric field domains in doped semiconductor superlattices is described within a microscopic model. Due to the presence of impurity bands in low-doped samples the current–voltage characteristic is essentially different compared to medium-doped samples.

Optically induced electric-field domains by bound-to-continuum transitions inn-type multiple quantum wells

We report on the experimental evidence of electric-field domain formation induced by the intersubband photocurrent in $n$-type $\mathrm{GaAs}/{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ multiple quantum wells. The domain structure manifests itself by a plateaulike regime in the voltage dependence of the total current under infrared illumination. Domain formation is caused by a negative differential field dependence of the photoexcited carrier mean free path. The domain structure does not exist in the dark since the increase of the thermally excited carrier density in the continuum overrides the decrease of the mean free path.

Photon assisted electric field domains in doped semiconductor superlattices

We study photon-assisted tunneling (PAT) through weakly-coupled doped semiconductor superlattices (SLs) in the high-voltage regime. A self-consistent model which treats the Coulomb interaction in a mean field approximation is considered. We discuss the formation of electric field domains in the presence of THz radiation and the appearance of new multistability regions caused by the combined effect of the strong nonlinearity coming from the Coulomb interaction and the new PAT channels. We show how the electric field domains can be supported by the virtual photonic sidebands due to multiple photon emission and absorption.

Switching and control of electric field configurations along multi-quantum well structures

The phenomenon of high-field domain formation and expansion along a superlattice/multi-quantum well system has been known since the first pioneering works on these structures. Experimentally it has usually been observed by monitoring negative differential resistance oscillations in the electric characteristics (I-V curves) of the samples. It is due to the fact that a uniform field distribution becomes unstable with respect to the formation of high and low electric field domains. When increasing the applied field, one can observe the progressive inducement of additional quantum well periods into the high-field domain, at voltages correlated with the alignment energies and with the periods of the oscillations in the I-V characteristics. Recently, optical tools were used to probe, in a more direct way, the field distributions along such systems. These experiments can be performed using interband or intersubband spectroscopies. The behaviour of electric field configurations along superlattices/multi-quantum well structures is strongly linked to the availability of free-space charge. Heavy doping or strong illumination providing this charge will induce stable field configurations. A supply of charge which is less than needed may result in a spatial oscillation of space charge among different sites. The regime of lowest charge supply can produce transient field domains resulting in spontaneous current oscillations reminiscent of transferred electron devices and Gunn diodes; however, the negative differential resistance driving the effect originates from low-dimensional transport properties rather than from bulk inter-valley transfer. In addition to its importance for transport studies, the presence of space-charge accumulation at definite sites along a superlattice/multi-quantum well system, together with the presence of different field domains, raise the possibility of spatial control, localization and/or modulation of optical nonlinear effects along such structures. We review previous studies, which used intersubband spectroscopy to study field domain switching, and present new results on how to use photoluminescence quenching of interband transitions, under the application of an applied field, to further investigate domain formation and expansion in multi-stack samples.

Impact of interface roughness on perpendicular transport and domain formation in superlattices

A microscopic calculation of the perpendicular current in doped multiple quantum wells is presented. Interface roughness is shown to affect the resonant transitions as well as to cause a nonresonant background current. The theoretical characteristics exhibit several branches due to the formation of electric field domains in quantitative agreement with experimental data.

Electric Field Domain Formation and Multistability in Semiconductor Multiple Quantum Wells in the Presence of THz Radiation

We propose a self-consistent microscopic model of vertical sequential tunneling through multiple quantum wells in the presence of THz radiation. The model considers the Coulomb interaction in a mean field approximation. We analyze the current density through a double quantum well and a superlattice and study the formation of electric field domains in the presence of THz radiation and the appearance of new multistability regions, both caused by the combined effect of the strong nonlinearity coming from the Coulomb interaction and the new photon-assisted tunneling channels. We show how the electric field domains can be supported by the virtual photonic sidebands due to multiple photon emission and absorption.

Microscopic model for sequential tunneling in semiconductor multiple quantum wells

We propose a selfconsistent microscopic model of vertical sequential tunneling through a multi-quantum well.The model includes a detailed description of the contacts,uses the Transfer Hamiltonian for expressions of the current and it treats the Coulomb interaction within a mean field approximation. We analyze the current density through a double well and a superlattice and study the formation of electric field domains and multistability coming from the Coulomb interaction. Phase diagrams of parameter regions (bias, doping in the heterostructure and in the contacts,etc) where the different solutions exist are given.

The effect of temperature on the resonant tunneling and electric field domain formation in multiple quantum well superlattices

Analyzing the photocurrent spectra and the I–V characteristics of weakly coupled GaAs/AlGaAs multiquantum well structures, different transport regimes are distinguished. At low temperatures (below ∼50 K), due to the electron coherence over a few periods of the superlattice, electron transport is dominated by sequential resonant tunneling. At higher temperatures, evidences for the increased contribution of nonresonant transport processes, and the subsequent modification in the electric field distribution in the device, are presented.

Electric-field domain formation in type-II superlattices.

Static electric-field domains as well as current self-oscillations due to domain-wall oscillations have been observed in undoped, type-II GaAs-AlAs superlattices under photoexcitation. Photoluminescence measurements clearly demonstrate the coexistence of low- and high-field domains in the static and oscillating domain voltage regime. A comparison with the calculated energy level distribution indicates that the static domains are connected with negative differential velocity (NDV) due to resonant transfer between ${X}_{2}$ in the AlAs layer and ${\ensuremath{\Gamma}}_{1}$ in the GaAs layer, while the oscillating domains are attributed to NDV originating from resonant tunneling between ${X}_{1}$ and ${X}_{2}$ in the AlAs layers. This observation demonstrates the importance of transport channels due to the indirect band structure of type-II superlattices.

Time-resolved photoluminescence investigations of electric-field domain formation in GaAs-AlAs superlattices.

The electric-field domain-formation time of an undoped GaAs-AlAs superlattice embedded in a ${\mathit{p}}^{+}$-i-${\mathit{n}}^{+}$ diode is investigated by time-resolved photoluminescence (PL). After optical excitation of electron-hole pairs with an ultrashort light pulse, the previously homogeneous electric field breaks up into domains that can be observed by a splitting of the PL line due to the quantum-confined Stark effect. The PL dynamics is studied as a function of excitation density and applied voltage. A domain-formation time on the order of a few nanoseconds is found. This time is unexpectedly short compared to the vertical transport time of electrons through the entire superlattice.

Quantum interference effect and electric field domain formation in quantum well infrared photodetectors

An observation of quantum interference effect in photocurrent spectra of a weakly coupled bound-to-continuum multiple quantum well photodetector is reported. This effect persists even at high biases where the Kronig–Penney minibands of periodic superlattice potential in the continuum are destroyed. Our results show that electrons remain coherent over a distance of 40–50 nm. The observation was used to investigate electric field domain formation induced by sequential resonant tunneling in the superlattice. A large off-resonant energy level alignment between two neighboring wells in the high field domain was observed.

Nonresonant carrier transport through high-field domains in semiconductor superlattices.

The actual field distribution in superlattices under electric field domain formation is investigated by photoluminescence and Raman spectroscopy. From the measured subband spacings, we determine the magnitude of the field that corresponds to resonant alignment of subbands in adjacent wells. The electron occupation of higher subbands is probed by photoluminescence (PL) measurements. Comparing the results of higher subband PL and the current-voltage characteristics, it is shown that the high-field domain is always nonresonantly coupled with a field strength below the resonance value. The sudden increase in the current when the high-field domain extends over the entire superlattice is explained. Calculations of the field distribution based on a microscopic model support our experimental observations.

Multistability of the current-voltage characteristics in doped GaAs-AlAs superlattices

Electric-field domain formation in doped semiconductor superlattices leads to sharp discontinuities in the current-voltage (I-V) characteristic. The successive expansion of the high-field region with increasing bias voltage through the periodic heterostructure manifests itself in a regular sequence of stable current branches. The current shows a complex hysteretic behavior. We observe two, three, and more stable current levels for fixed bias voltages. Calculations of the I-V characteristic based on a microscopic model support the experimentally observed multistability.

Control of electric field domain formation in multiquantum well structures

The formation, expansion, and readjustment of electric field domains in multiquantum well stacks is described and explained in terms of sequential resonant tunneling. These effects are used to control the multiband spectral response in IR detector applications of these structures.

Voltage-controlled tunable GaAs/AlGaAs multistack quantum well infrared detector

We describe a new type of intersubband GaAs/AlGaAs infrared detector consisting of three stacks of quantum wells; the quantum wells in a given stack are identical, but are different from stack to stack. Each stack is designed to yield an absorption and a photoresponse at a different peak wavelength. The resulting device is an infrared detector which can operate in a number of modes. Among the features of this device are a wide-band detection domain, a tunable response and excellent responsivities and noise figures. The tunable operation includes a sharp peak-switching response which follows the formation, expansion, and readjustment of electric field domains within the multiquantum well region.