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1.
Spontaneous and piezoelectric polarization in hexagonal GaN/AlGaN heterostructures give rise to large built-in electric fields.
The effect of the builtin electric field in GaN/Al xGa 1−xN quantum wells was investigated for x=0.2 to 0.8 by photoluminescence studies. The quantum well structures were grown by
molecular beam epitaxy on (0001) sapphire substrates. Cross-sectional transmission electron microscopy performed on the samples
revealed abrupt interfaces and uniform layer thicknesses. The low temperature (4 K) photoluminescence peaks were progressively
red-shifted due to the quantum confined Stark effect depending on the AlN mole fraction in the barriers and the thickness
of the GaN quantum well. Our results verify the existence of very large built-in electric fields of up to 5 MV/cm in GaN/Al 0.8Ga 0.2N quantum wells. 相似文献
2.
Aluminum gallium nitride-based double heterostructures with two different active layer widths have been grown on GaN templates by metalorganic chemical vapor deposition. Crystalline quality has been investigated using high-resolution x-ray diffraction analysis, and screw, edge, as well as total dislocation densities in the GaN epilayer have been calculated. The dislocation density of GaN has been found to be on the order of 10 8 cm ?2. The nominal Al composition and in-plane strain ε xx for the AlGaN layer grown on the GaN layer have been measured by asymmetric reciprocal-space mapping. Surface properties and cross-sectional views of the samples have been analyzed using atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM), respectively. Room-temperature time-resolved photoluminescence and photoluminescence measurements have been performed on Al 0.18Ga 0.82N/Al 0.45Ga 0.55N double heterostructures and the GaN template. The interface recombination velocity ( S) of AlGaN-based double heterostructures has been calculated using carrier decay time measurement, increasing from 8.7 × 10 3 cm/s to 13.4 × 10 3 cm/s with varying active layer thickness. 相似文献
3.
The transition from two-dimensional (2D) pseudomorphic growth to the three-dimensional (3D) (nanoisland) growth in In xGa 1?xAs/GaAs multilayer structures grown by molecular-beam epitaxy was investigated by atomic force microscopy, photoluminescence, and Raman scattering. The nominal In content x in In xGa 1?xAs was varied from 0.20 to 0.50. The thicknesses of the deposited In xGa 1?xAs and GaAs layers were 14 and 70 monolayers, respectively. It is shown that, at these thicknesses, the 2D-3D transition occurs at x ≥ 0.27. It is ascertained that the formation of quantum dots (nanoislands) does not follow the classical Stranski-Krastanov mechanism but is significantly modified by the processes of vertical segregation of In atoms and interdiffusion of Ga atoms. As a result, the In xGa 1?xAs layer can be modeled by a 2D layer with a low In content ( x < 0.20), which undergoes a transition into a thin layer containing nanoislands enriched with In ( x > 0.60). For multilayer In xGa 1?xAs structures, lateral alignment of quantum dots into chains oriented along the \([\overline 1 10]\) direction can be implemented and the homogeneity of the sizes of quantum dots can be improved. 相似文献
4.
The electric fields in Al 0.3Ga 0.7N/Al 0.4Ga 0.6N quantum wells are estimated. The quantum wells are grown by plasma-assisted molecular-beam epitaxy with plasma activation of nitrogen. The three-dimensional and planar modes of buffer layer growth are used. The transition to the three-dimensional mode of growth yields a substantial increase in the photoluminescence intensity of the quantum wells and a shift of the photoluminescence line to shorter wavelengths. These effects are attributed to the fact that, because of the extra three-dimensional localization of charge carriers in the quantum-well layer, the quantum-confined Stark effect relaxes. The effect of localization is supposedly due to spontaneous composition fluctuations formed in the AlGaN alloy and enhanced by the three-dimensional growth. 相似文献
5.
The growth peculiarities of In 0.8Ga 0.2As quantum dots and their arrays on GaAs surface by metalorganic vapor-phase epitaxy are investigated. The bimodal size distribution of In 0.8Ga 0.2As quantum dots is established from the photoluminescence spectra recorded at different temperatures. The growth parameters were determined at which the stacking of 20 In 0.8Ga 0.2As quantum-dot layers in the active area of a GaAs solar cell makes it possible to enhance the photogenerated current by 0.97 and 0.77 mA/cm 2 for space and terrestrial solar spectra, respectively, with the high quality of the p–n junction retained. The photogenerated current in a solar cell with quantum dots is higher than in the reference GaAs structure by ~1% with regard to nonradiative-recombination loss originating from stresses induced by the quantum-dot array. 相似文献
6.
Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al x Ga 1 ? x N/Al y Ga 1 ? y N quantum wells. Structural and optical properties of the Al x Ga 1 ? x N layers in the entire range of compositions ( x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al 2O 3 substrates, heterostructures for light-emitting diodes with Al x Ga 1 ? x N/Al y Ga 1 ? y N quantum wells ( x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm. 相似文献
7.
The deposition of In x Ga 1–x As with an indium content of 0.3–0.5 and an average thickness of 3–27 single layers on a GaAs wafer by metalorganic chemical vapor deposition (MOCVD) at low temperatures results in the appearance of thickness and composition modulations in the layers being formed. Such structures can be considered to be intermediate nanostructures between ideal quantum wells and quantum dots. Depending on the average thickness and composition of the layers, the wavelength of the photoluminescence peak for the hybrid InGaAs quantum well–dots nanostructures varies from 950 to 1100 nm. The optimal average In x Ga 1–x As thicknesses and compositions at which the emission wavelength is the longest with a high quantum efficiency retained are determined. 相似文献
8.
Features of the growth of InAs quantum dots in an Al 0.35Ga 0.65As matrix by molecular beam epitaxy at different substrate temperatures, deposition rates, and amounts of deposited InAs are studied. The optimum conditions for growing an array of low-density (≤2 × 10 10 cm ?2) small (height of no more than 4 nm) self-organized quantum dots are determined. The possibility of the formation of optically active InAs quantum dots emitting in the energy range 1.3–1.4 eV at a distance of no more than 10 nm from the coherent heterovalent GaAs/ZnSe interface is demonstrated. It is established that inserting an optically inactive 5-nm GaAs quantum well resonantly coupled with InAs quantum dots into the upper AlGaAs barrier layer enhances the photoluminescence efficiency of the quantum-dot array in hybrid heterostructures. 相似文献
9.
High quality Si-doped n-Al 0.6Ga 0.4N thin films were grown on sapphire substrates by molecular beam epitaxy (MBE) by interrupted deposition and subsequent in-situ thermal annealing (IDTA). High-resolution X-ray diffraction, scanning electron microscope, atomic force microscope, photoluminescence and Hall-effect measurements were carried out to characterize the structural, electrical and optical properties. The results showed that the full width at half-maximum of the Si-doped Al 0.6Ga 0.4N (0002) was as low as 160 arcsec. The threading dislocation density decreases two orders of magnitude to 6×110 7 cm −2 by using the IDTA technology. The carrier density and mobility reached at 1.1×10 19 cm −3 and 4.8 cm 2/V s, respectively. Si still acted as a shallow donor even for the heavily doped Al 0.6Ga 0.4N. 相似文献
10.
Electronic and optical properties are obtained with the increase in indium alloy content ( x) in a Ga 1-xIn xN/Al 0.2Ga 0.8N quantum dot. The barrier height with the different In alloy contents is applied to acquire the confinement potentials. The results are obtained taking into consideration geometrical confinement effect. The optical absorption coefficient with the photon energy is observed in a Ga 1-xIn xN/Al 0.2Ga 0.8N quantum dot. The optical output with the injection current density and the threshold optical pump intensity for various In alloy contents are studied. The differential gain as functions of indium alloy content, charge density and the dot radii in the Ga 1-xIn xN/Al 0.2Ga 0.8N quantum dot are investigated. The exciton binding energy is calculated in order to obtain the exciton density, the optical gain and the threshold current density in the Ga 1-xIn xN/Al 0.2In 0.8N quantum dot. The results show that the red shift energy with an increase in In alloy content is found and the differential gain increases with the charge carrier density. 相似文献
11.
Tertiarybutylarsine (TBA) and teriarybutylphosphine (TBP) are liquid organometallic sources that are a safer alternative to
arsine and phosphine. In this work, we have grown high-quality In 0.53Ga 0.47As/InP quantum wells at a temperature of 590° with TBA and TBP partial pressures of 0.4 and 2.5 Torr, respectively. A low-temperature
photoluminescence study indicated optimized column V growth interruption times of 0.5 s for In 0.53Ga 0.47As wells with InP barriers. Using the optimized growth conditions, we have obtained lattice matched In 0.53Ga 0.47As/In xGa 1-xAs yP 1-x single quantum-well lasers emitting at 1.55 μm. Broad-area devices with a length of 3.5 mm exhibit a low threshold current
density of 220A/cm 2. Broad-area lasers containing four quantum wells had a threshold current density of 300A/cm 2 for a 3.0 mm cavity length and CW powers of 40 mW per facet for an as-cleaved 4 × 750 μm device. 相似文献
12.
Results of photoluminescence (PL) studies of self-organized nanoscale InP islands (quantum dots, QDs) in the In 0.49Ga 0.51P matrix, grown on a GaAs substrate by metalorganic vapor phase epitaxy (MOVPE), are presented. Dependences of the PL efficiency
on temperature in the range 77–300 K and on excitation level at pumping power densities of 0.01–5 kW/cm 2 have been obtained. The PL spectra are a superposition of emission peaks from QDs and the wetting layer. Their intensity
ratio depends on the pumping power and temperature, and the emission wavelength varies in the range 0.65–0.73 μm. At 77 K
and low excitation level, InP QDs exhibit high temperature stability of the emission wavelength and high quantum efficiency.
__________
Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 2, 2001, pp. 242–244.
Original Russian Text Copyright ? 2001 by Vinokurov, Kapitonov, Nikolaev, Sokolova, Tarasov. 相似文献
13.
Dependences of spectra, intensity, and relaxation time of superradiance in GaAs/In xGa 1?xAs/GaAs quantum heterostructures on the excitation power density in the range of 1×10 ?3–1×10 6 W/cm 2 are investigated. It is shown for the first time that filling of the quantum well affects all spectral characteristics of superradiance. 相似文献
14.
Hybrid quantum-confined heterostructures grown by metal-organic vapor-phase epitaxy (MOVPE) via the deposition of In 0.4Ga 0.6As layers with various nominal thicknesses onto vicinal GaAs substrates are studied by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence spectra of these structures show the superposition of two spectral lines, which is indicative of the bimodal distribution of the size and/or shape of light-emitting objects in an array. The dominant spectral line is attributed to the luminescence of hybrid “quantum well–dot” nanostructures in the form of a dense array of relatively small quantum dots (QDs) with weak electron and hole localization. The second, lower intensity line is attributed to luminescence from a less dense array of comparatively larger QDs. Analysis of the behavior of the spectral line intensities at various temperatures showed that the density of larger QDs grows with increasing thickness of the InGaAs layer. 相似文献
15.
GaInAsSb and AlGaAsSb alloys have been grown by organometallic vapor phase epitaxy (OMVPE) using all organometallic sources,
which include tritertiarybutylaluminum, triethylgallium, trimethylindium, tertiarybutylarsine (TBAs), and trimethylantimony.
Excellent control of lattice-matching both alloys to GaSb substrates is achieved with TBAs. GaInAsSb/AlGaAsSb multiple quantum
well (MQW) structures grown by OMVPE exhibit strong 4K photoluminescence with full width at half maximum of 10 meV, which
is comparable to values reported for quantum well (QW) structures grown by molecular beam epitaxy. Furthermore, we have grown
GaInAsSb/AlGaAsSb MQW diode lasers which consist of n- and p-doped Al 0.59Ga 0.41As 0.05Sb 0.95 cladding layers, Al 0.28Ga 0.72As 0.02Sb 0.98 confining layers, and four 15 nm thick Ga 0.87In 0.13As 0.12Sb 0.88 quantum wells with 20 nm thick Al 0.28Ga 0.72As 0.02Sb 0.98 barrier layers. These lasers, emitting at 2.1 μm, have exhibited room-temperature pulsed threshold current densities as low
as 1.2 kA/cm 2. 相似文献
16.
The results of the investigation of low-temperature time-resolved photoluminescence in undoped and Si-doped In 0.2Ga 0.8N/GaN structures, which contain 12 quantum wells of width 60 Å separated by barriers of width 60 Å, are reported. The structures were grown by the MOCVD technique on sapphire substrates. The photoluminescence properties observed are explained by the manifestation of two-dimensional donor-acceptor recombination. These properties are the high-energy shift of the peak upon increasing the pumping intensity, a low-energy shift with increasing delay time, and a power law of luminescence decay of the t -γ type. The estimates of the total binding energy for donor and acceptor centers are given. This energy is 340 and 250 meV for Si-doped and undoped quantum wells, respectively. The role of the mosaic structure, which is typical for Group III hexagonal nitrides, is discussed as a factor favorable for the formation of donor-acceptor pairs. 相似文献
17.
In this work, we investigate the formation of the inverted technology created quantum dot by a method based on droplet epitaxy. The preparation process of the so called inverted quantum dot is carried out with the filling of the nano-hole. The investigated GaAs dot is embedded in AlAs/Al xGa 1 − xAs multilayer structure. Transmission electron microscopy investigation shows that the quantum structure is perfectly crystalline and fits very well to the crystal structure of the base layer. The nano-hole has a hill around its opening. Furthermore, the sides of the nano-structure consist of low Miller index facets. The filling process results formation of a hill over the nano-hole. The elemental mapping shows Al immigration into the GaAs layer. Formation of the hill after the filling process and the Al immigration are also explained in this paper. Temperature dependent photoluminescence spectra were measured in the range of room temperature and 4.7 K. The electronic structure given from photoluminescence spectroscopy is explained. 相似文献
18.
The spatial distribution of photocurrent in the plane of a Si-based p
+–n junction with embedded self-assembled Ge
x
Si1–x
(x ≈ 0.35) nanoislands is studied by scanning near-field optical microscopy with local photoexcitation by a microscope probe at an emission wavelength of 1310 nm (larger than the intrinsicphotosensitivity red edge for Si). Inhomogeneities related to interband optical absorption in separate GeSi nanoislands are observed in the photocurrent images (maps of the spatial distribution of the photocurrent in the input-window plane of the p
+–n photodiodes). The results of this study demonstrate the possibility of visualizing individual GeSi nanoislands in images of the photocurrent with a spatial resolution of ~100 nm. 相似文献
19.
We have grown In 0.5Ga 0.5N films on SiO 2/Si (100) substrate at 100–400 °C for 90 min by rf reactive sputtering with single cermet target. The target was made by hot pressing the mixture of metallic indium, gallium and ceramic gallium nitride powder. X-ray diffraction (XRD) measurements indicated that In 0.5Ga 0.5N films had wurtzite structure and showed the preferential (1 0 -1 0) diffraction. Both SEM and AFM showed that In 0.5Ga 0.5N films were smooth and had small roughness of 0.6 nm. Optical properties were measured by photoluminescence (PL) spectra from room temperature to low temperature of 20 K. The 2.28 eV green emission was achieved at room temperature for all our InGaN films. The electrical properties of In 0.5Ga 0.5N films on a SiO 2/Si (100) substrate were measured by the Hall measurement at room temperature. InGaN films showed the electron concentration of 1.51×10 20–1.90×10 20 cm −3 and mobility of 5.94–10.5 cm 2 V −1 s −1. Alloying of InN and GaN was confirmed for the sputtered InGaN. 相似文献
20.
Temperature-gradient metalorganic chemical vapor deposition (MOCVD) was used to deposit In xGa 1−xN/GaN multiple quantum well (MQW) structures with a concentration gradient of indium across the wafer. These MQW structures
were deposited on low defect density (2×10 8 cm −2) GaN template layers for investigation of microstructural properties and V-defect (pinhole) formation. Room temperature (RT)
photoluminescence (PL) and photomodulated transmission (PT) were used for optical characterization, which show a systematic
decrease in emission energy for a decrease in growth temperature. Triple-axis x-ray diffraction (XRD), scanning electron microscopy,
and cross-sectional transmission electron microscopy were used to obtain microstructural properties of different regions across
the wafer. Results show that there is a decrease in crystal quality and an increase in V-defect formation with increasing
indium concentration. A direct correlation was found between V-defect density and growth temperature due to increased strain
and indium segregation for increasing indium concentration. 相似文献
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