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The study investigates high-voltage gradual p0–i–n0 junctions in solid solutions of AlxGa1 – xAs1 – ySby with y up to 15%, which are capable of absorbing radiation with a wavelength of 1064 nm, grown on GaAs substrates by liquid-phase epitaxy through self-doping with background impurities. The composition of the liquid phase and the temperature range of growth are selected so that the aluminum-compound content x decreased steadily from the specified values of about 34% to a few percent at the surface of the epitaxial layer, while the antimony-compound content y increased. In this case, the band-gap width gradually decreased from the substrate to the surface of the lightly doped layer, reaching the desired value of ~1.16 eV. By measuring the capacity–voltage characteristics and deep level transient spectroscopy in them, configurationally bistable DX centers associated with donor impurities Si and Se/Te are identified. The investigated heterophase epitaxial layers reveal the absence of deep energy levels associated with dislocations. The effective lifetime of minority charge carriers in the base layers of the AlxGa1 – xAs1 – ySby/GaAs diode is determined using reverse recovery of the diode. Assuming that the minority-carrier lifetime is mainly determined by the capture of holes by the acceptor-like deep level DX – of Si in the n0 layer of the material, the hole capture cross section on the DX – level is estimated. The capture cross section is found to be 6 × 10–15 cm2. [ABSTRACT FROM AUTHOR]

High-voltage gradual p0–i–n0 junctions of AlxGa1 –xAs1 –ySby with x ~ 0.24 and y ~ 0.05 in the i‑region were studied using capacitance-voltage characteristics method and transient spectroscopy of deep levels. It has been established that the effective recombination trap in them is the DX-center of the Si donor impurity, with a thermal activation energy Et = 414 meV, a capture cross section σn = 1.04 × 10–14 cm2, and a concentration Nd = 2.4 × 1015 cm–3. In the heterostructures studied, there were no deep levels associated with dislocations. [ABSTRACT FROM AUTHOR]

We present the results of experimental studies of the capacitance–voltage (C–V) characteristics and the spectra of deep-level transient spectroscopy (DLTS) of graded high-voltage p+–p0–i–n0 GaAs diodes fabricated by liquid-phase epitaxy at a crystallization-onset temperatures of 900°C from one solution melt due to self doping with background impurities, in a hydrogen or argon atmosphere, before and after irradiation with neutrons. After irradiation with neutrons, the DLTS spectra reveal wide defect-cluster regions with acceptor-like negatively charged traps of the n0-type layer, resulting from the emission of electrons from states located above the middle of the band gap. It is found that the differences in the C–V characteristics of the structures grown in a hydrogen or argon atmosphere are due to the different doses of irradiation of p+–p0–i–n0 GaAs structures and different degrees of compensation of shallow donor impurities by deep traps in the layers. [ABSTRACT FROM AUTHOR]

The temperature dependences of the capacitance-voltage (C–V) characteristics and deep-level spectra of a graded high-voltage AlxGa1 –xAs p0–i–n0 junction grown by liquid-phase epitaxy via autodoping with background impurities are studied. Changes in the C–V characteristics at varied measurement temperature and optical illumination demonstrate that the p0-, i-, and n0-type layers in AlxGa1 –xAs under study contain bistable DX centers. Spectra furnished by deep-level transient spectroscopy (DLTS), measured at various bias voltages Vr and filling-pulse voltages Vf, show a positive DLTS peak for the n0-type layer, with a thermal activation energy of Et = 280 meV and electron-capture cross section of σn = 3.17 × 10–14 cm2, which is unusual for a majority-charge-carrier trap. This peak is attributed to the negatively charged state of the Se/Te donor impurity, which is a bistable DX center with negative correlation energy U. [ABSTRACT FROM AUTHOR]

The temperature dependences of the capacitance–voltage characteristics and deep-level spectra of a Au–n-Si:Au–Si–p-Si heterostructure based on a composite layer of Au and Si nanoparticles are investigated. The structure manifests the properties of a transistor connected to a circuit with a common emitter with a disconnected base and an emitter Schottky barrier between the Au point contact and the n–(Si:Au) layer. Nanoparticles in this layer form finite clusters with hopping conductivity; herewith, charge accumulation is observed in the region of the Au point contact. The system at a measurement temperature below 180 K transitions from the finite-cluster phase to the infinite-cluster phase due to the percolation effect. This phase manifests metallic properties in the lateral plane of the heterostructure, which transforms into a p–n diode. [ABSTRACT FROM AUTHOR]

C-V characteristics and DLTS spectra of heterostructures made up of layers of closely packed amorphous Si nanoparticles deposited by laser electrodispersion onto single-crystal p-Si substrates have been examined. The patterns observed in the behavior of the C-V characteristics and DLTS spectra measured in the dark and under illumination with white light at various bias pulse voltages Ub and filling pulse voltages Uf suggest that the spatially localized amorphous Si nanoparticles have an average size of less than 2 nm, which is comparable with the de Broglie electron wavelength, and are characterized by quantum confinement. The ground and excited states of quantum dots are formed and exhibit the Stark effect and effects of electricdipole and controllable metastable occupancy under illumination. [ABSTRACT FROM AUTHOR]

Electron and hole emission from states of a ten-layer system of tunneling-coupled vertically correlated InAs/GaAs quantum dots (QDs) is studied experimentally by capacitance—voltage measurements and deep-level transient spectroscopy. The thickness of GaAs interlayers separating sheets of InAs QDs was ≈3 nm, as determined from transmission electron microscope images. It is found that the periodic multimo-dal DLTS spectrum of this structure exhibits a pronounced linear shift as the reverse-bias voltage Ur applied to the structure is varied. The observed behavior is a manifestation of the Wannier—Stark effect in the InAs/GaAs superlattice, where the presence of an external electric field leads to the suppression of coupling between the wave functions of electron states forming the miniband and to the appearance of a series of discrete levels called Wannier—Stark ladder states. [ABSTRACT FROM AUTHOR]

The absorption of uncoupled and tunnel-coupled vertically correlated quantum dots (QDs), measured at room temperature, has been experimentally compared. It is revealed that matching of the laser wavelength and Stark shift for laser structures with tunnel-coupled QDs leads to resonant absorption with formation of bound and antibound exciton states with a splitting energy of ∼62 meV between them in QD molecules. For these states, an external field causes a large linear Stark shift (up to 68 meV). For uncoupled QDs, one resonant absorption peak with the formation of an exciton (for which the Stark shift does not exceed 13 meV) is observed. [ABSTRACT FROM AUTHOR]

Deep level transient spectroscopy (DLTS) measurements were performed to study electron emission from quantum states in a 20-layer Ge quantum-dot superlattice (QDSL) in a Ge/Si p-n heterostructure. It was established that the changes in the DLTS spectra depend heavily on the magnitude of the applied reverse bias U r . Three regions of the reverse bias U r were identified, corresponding to the manifestation of the three modes of the Wannier-Stark effect: Wannier-Stark ladder mode, Wannier-Stark localization, and nonresonant Zener tunneling mode. Furthermore, it was found that the appearance of DLTS peaks for all three modes is associated with electron emission from deep-level defects via Wannier-Stark localized states arising as a result of the splitting of the electron miniband of the Ge/Si QDSL. [ABSTRACT FROM AUTHOR]

Blue light-emitting diodes (LEDs) based on InGaN/GaN quantum wells (QWs) with different characters of the system of extended defects (SEDs) threading through the active region have been studied using the current-voltage ( I–U), capacitance-voltage ( C–V), and deep-level transient spectroscopy (DLTS) measurements in the dark and under illumination with white light in a temperature range from 100 to 450 K. The DLTS curves exhibit broad E1 and E2 peaks with amplitudes dependent on the illumination. This behavior can be explained assuming the presence of localized states related to SEDs in the active region of the LED. The LEDs with more developed SEDs are characterized by a greater concentration of donor-type traps, which leads to an increase in the density of free charge carriers in QWs, which screen the electron-hole interaction. This circumstance can be among the factors responsible for a severalfold decrease in the quantum efficiency of such LEDs. [ABSTRACT FROM AUTHOR]

Deep level transient spectroscopy (DLTS) is used to study electron emission from the states in the system of vertically correlated InAs quantum dots in the p-n InAs/GaAs heterostructures, in relation to the thickness of the GaAs spacer between the two layers of InAs quantum dots and to the reverse-bias voltage. It is established that, with the 100 Å GaAs spacer, the InAs/GaAs heterostructure manifests itself as a system of uncoupled quantum dots. The DLTS spectra of such structures exhibit two peaks that are defined by the ground state and the excited state of an individual quantum dot, with energy levels slightly shifted (by 1–2 eV), due to the Stark effect. For the InAs/GaAs heterostructure with two layers of InAs quantum dots separated by the 40 Å GaAs spacer, it is found that the quantum dots are in the molecule-type phase. Hybridization of the electron states of two closely located quantum dots results in the splitting of the levels into bonding and antibonding levels corresponding to the electron ground states and excited states of the 1 s +, 1 s −, 2 p +, 2 p −, and 3 d + types. These states manifest themselves as five peaks in the DLTS spectra. For these quantum states, a large Stark shift of energy levels (10–40 meV) and crossing of the dependences of the energy on the electric field are observed. The structures with vertically correlated quantum dots are grown by molecular beam epitaxy, with self-assembling effects. [ABSTRACT FROM AUTHOR]

Deep-level transient spectroscopy is used to study charge-carrier emission from the states of separate quantum dots in InAs/GaAs p–n heterostructures grown on (100)- and (311)A-oriented GaAs substrates in relation to the reverse-bias voltage U. It is established that the structures under consideration exhibit different bias-voltage dependences of the Stark shift for the energy levels of the quantum-dot states on the value of U. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Deep-level transient spectroscopy is used to study the emission of holes from the states of a vertically coupled system of InAs quantum dots in p-n InAs/GaAs heterostructures. This emission was considered in relation to the thickness of a GaAs interlayer between two layers of InAs quantum dots and to the reverse-bias voltage Ur. It is established that hole localization at one of the quantum dots is observed for a quantum-dot molecule composed of two vertically coupled self-organized quantum dots in an InAS/GaAs heterostructure that has a 20-A-thick or 40-A-thick GaAs interlayer between two layers of InAs quantum dots. For a thickness of the GaAs interlayer equal to 100 A, it is found that the two layers of quantum dots are incompletely coupled, which results in a redistribution of the hole localization between the upper and lower quantum dots as the voltage Ur applied to the structure is varied. The studied structures with vertically coupled quantum dots were grown by molecular-beam epitaxy using self-organization effects. [ABSTRACT FROM AUTHOR]

The effect of In and Al on the properties of the As[sub Ga] defect complex (arsenic substituted for gallium at a crystal lattice site) in GaAs-based quantum dots (QDs) was investigated using the nonempirical quantum-chemical SCF–MO–LCAO technique. It is shown that an As[sub Ga] defect can exist in stable and metastable states. Raising the indium or aluminum content in QD enhances the probability of As[sub Ga] defect formation in the stable state; in case of In introduction, this effect is manifested more strongly. The activation energy of the transition between stable and metastable states varies between 0.886 and 2.049 eV, depending on the QD stoichiometry. The formation of an As[sub Ga] defect gives rise to two deep levels in the band gap. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

The results of studies of hole energy states in vertically coupled quantum dots in InAs-GaAs p-n heterostructures by deep-level transient spectroscopy are reported. Spectra were recorded at different reverse-bias voltages. Levels related to bonding and antibonding s and p states of vertically coupled quantum dots were revealed. The energies of these states significantly depend on an external electric field applied to a heterostructure. This dependence was attributed to the quantum-dimensional Stark effect for the hole states of vertically coupled quantum dots. In addition to this, it was found that the energy of thermal activation of carriers from vertically coupled quantum dots depends on the conditions of isochronous annealing that was carried out both with the reverse bias switched-on and switched-off and both in the presence and absence of illumination. These changes, as in the case of isolated quantum dots, are typical of a bistable electrostatic dipole formed by carriers, localized in a coupled quantum dot, and ionized lattice point defects. The built-in electric field of this dipole reduces the energy barrier for the carriers in the coupled quantum dot. The investigated structures with vertically coupled quantum dots were grown using molecular-beam epitaxy taking account of self-assembling effects. [ABSTRACT FROM AUTHOR]

The electron emission from and capture by quantum dots in InGaAs/GaAs p-n heterostructures were studied using deep-level transient spectroscopy in relation to the conditions of isochronous annealing with a switched-on or -off bias voltage (U[sub ra] < 0 or U[sub ra] = 0). The results indicate that, as a result of annealing with U[sub ra] < 0, a dipole that consists of charge carriers localized in the quantum dots and the ionized lattice defects is formed. The electrostatic potential of this dipole reduces the barrier for the electron emission from and capture by a quantum dot. If the annealing is performed at U[sub ra] = 0, no dipole is formed and the band offset is controlled by the conditions of heteroboundary formation during the structure growth. The dependence of the barrier height on the filling-pulse duration was also observed; this dependence is related to the manifestation of the Coulomb blockade for the electron capture by the ground and excited states of a quantum dot. The structures with quantum dots studied were grown by gaseous-phase epitaxy from metal-organic compounds using self-organization effects. [ABSTRACT FROM AUTHOR]

A report is presented on the investigation of the influence of in situ annealing of the InGaAs layer in p-n InGaAs/GaAs structures grown by the metalloorganic chemical vapor deposition upon the formation of coherently strained three-dimensional islands. The structures were studied by the methods of capacitance-voltage measurements, deep-level transient spectroscopy, transmission electron microscopy, and photoluminescence. It is established that three-dimensional islands with misfit dislocations are formed in the unannealed structure A, while quantum dots are formed in the annealed structure B. The deep-level defects were investigated. In structure A, defects of various types (EL2, EL3 (I3), I2, HL3, HS2, and H5) are present in the electronaccumulation layer. Concentrations of these traps are comparable to the shallow donor concentration, and the number of hole traps is higher than that of the electron traps. On the in situ annealing, the EL2 and EL3 defects, which are related to the formation of dislocations, disappear, and concentrations of the other defects decrease by an order of magnitude or more. For structure A, it is established that the population of the quantum states in the islands is controlled by the deep-level defects. In structure B, the effect of the Coulomb interaction of the charge carriers localized in the quantum dot with the ionized defects is observed. [ABSTRACT FROM AUTHOR]

The results of a study of a structure with a single array of InAs quantum dots in a GaAs matrix using capacitance-voltage measurements, deep-level transient spectroscopy (DLTS), photoluminescence spectroscopy, and transmission electron microscopy are reported. Clusters of interacting bistable defects are discovered in GaAs layers grown at low temperature. Controllable and reversible metastable populating of quantum-dot energy states and monoenergetic surface states, which depends on the temperature and conditions of a preliminary isochronal anneal, is observed. This effect is associated with the presence of bistable traps with self-trapped holes. The DLTS measurements reveal variation of the energy for the thermal ionization of holes from surface states of the InAs/GaAs heterointerface and the wetting layer as the reverse bias voltage is increased. It is theorized that these changes are caused by the built-in electric field of a dipole, which can be formed either by wetting-layer holes or by ionized levels located near the heterointerface. [ABSTRACT FROM AUTHOR]

Indium arsenide/gallium arsenide structures with vertically coupled quantum dots imbedded in the active zone of a laser diode are investigated by deep-level transient spectroscopy (DLTS), and the capacitance-voltage characteristics are analyzed. The DLTS spectrum was found to undergo significant changes, depending on the temperature of preliminary isochronous annealing of the sample, T[sub a] < T[sub ac] = 245 K or T[sub a] > T[sub ac], and on the cooling conditions, with a bias voltage V[sub b] = 0 or with an applied carrier pulse V[sub f] > 0. The changes are attributed to the onset of Coulomb interaction of carriers trapped in a quantum dot with point defects localized in the nearest neighborhoods of the quantum dots and also to the formation of a dipole when T[sub a] < T[sub ac] and cooling takes place with V[sub f] > 0, or to the absence of a dipole when T[sub a] > T[sub ac] and V[sub b] = 0. It is discovered that the tunneling of carriers from the deeper states of defects to the shallower states of quantum dots takes place in the dipole, and the carriers are subsequently emitted from the dots into bands. [ABSTRACT FROM AUTHOR]

Microstructures in p–CuInSe[sub 2] single crystals tailored by the strong electric field have been studied using the method of local (d≲1 μm) cathodoluminescence (CL). The shortest-wavelength radiation (hω=1.023 eV) has been observed from the n-type layer and longer-wavelength radiation (hω=1.006 eV)—from the p-type regions. An analysis of the cathodoluminescence spectra has allowed us to attribute the experimental features to optical transitions associated with donor and acceptor levels of V[sub Cu],V[sub Se], and Cu[sub i] point defects in the crystal. Test measurements of EBIC, the C–V characteristics, and the DLT spectra confirm the cathodoluminescence data and reveal additional features of the p–n–p microstructures. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Stark effect has been studied in multilayer InGaAs/GaAs laser structures with self-assembled quantum dots (QDs). A shift in the absorption edge depending on the reverse bias voltage has been measured in a two-section laser diode. The QD absorption edge shifts toward longer wavelengths with increasing electric field strength. It is established that the QD absorption depends on the polarization of light. The intensity at which TE-polarized luminescence in laser structures is studied is more than ten times higher than that of the TE-polarized emission component, which is explained by higher amplification of the TE mode. [ABSTRACT FROM AUTHOR]

Electron emission in a system of vertically coupled quantum dots (VCQDs) in InAs/GaAs p- n-heterostructures obtained by molecular beam epitaxy has been studied by means of deep-level transient spectroscopy (DLTS) as a function of the number of quantum dot (QD) rows and the reverse bias voltage. For a GaAs spacer thickness of d GaAs = 40 Å, the system occurs in a molecular state, irrespective of the number of QD rows. An increase in this number leads to a decrease in the Stark shift, which is probably related to a decrease in the lattice strain potential in the vicinity of VCQDs. [ABSTRACT FROM AUTHOR]

Deep-level transient spectroscopy was used to study the parameters of deep levels in the band gap of epitaxial n-GaN layers after irradiaton of the Schottky barriers with 1-MeV protons to a dose of 10[sup 12] cm[sup -2]. A deep level EP1 with an activation energy of 0.085 eV was introduced by irradiation into the upper half of the GaN band gap. The introduction rate of the corresponding defect was found to depend on the bias voltage applied to the Schottky barrier during irradiation. [ABSTRACT FROM AUTHOR]

The preparation of pure, undoped, high-temperature GaP grown by liquid-phase epitaxy is reported. Results are presented of studies of GaP p-n structures grown at various crystallization initiation temperatures, using the capacitance-voltage (C-V) method and deep-level transient spectroscopy (DLTS). The characteristics of GaP are determined by the low concentration of background impurities and deep-level defects. Measurements of the temperature dependence of the forward branch of the current-voltage characteristic showed that the thermometric characteristic of the diode is linear between -191 and ∼+600 °C. [ABSTRACT FROM AUTHOR]