AlGaAs Heterostructures Research Articles

Growth of GaSb / AlSb heterostructures on patterned substrates by molecular beam epitaxy

InAs / AlSb / GaSb heterostructures with excellent morphological and electrical properties were regrown for the first time on dry-etched GaAs substrates and GaSb epilayers. The shape of the overgrown structures is determined by the adatom species, the crystallographic direction and the growth parameters. For stripe orientations in [011], [001] and [0 1 1] directions, only (111), (110) and (100) planes are formed near the stripe edges. No higher index facets were observed, in contrast to regrowth of GaAs / AlGaAs heterostructures on patterned wafers. Significant differences in growth rates are observed for GaSb and AlSb on (111)A and (111)B facets. On (111)A planes, GaSb and AlSb grow with nearly the same growth rate. However, the growth rate of GaSb on (111)B facets is drastically reduced due to the enhanced migration of Ga from (111)B planes to (100) planes with a higher sticking coefficient for Ga. No degradation of the electrical properties of InAs quantum well structures is observed after regrowth on dry-etched GaSb epilayers, thus proving the suitability of the patterning process.

Anisotropic electron cyclotron resonance etchingof GaInP/AlGaInP heterostructures

Anisotropic dry etching of GaInP/AlGaInP heterostructures has been achieved for the first time in a high-ion-density electron cyclotron resonance (ECR)-generated plasma. Structures consisting of AlInP/(GaInP/AlGaInP)/AlInP and AlGaAs/(GaInP/AlGaInP)/AlGaAs heterostructures have been etched in a CH4/H2/Cl2/BCl3/Ar plasma with smooth sidewalls and surface morphologies.

Intraminiband plasmons in a superlattice within a parabolic well

A well defined collective plasma resonance corresponding to electrons tunneling back and forth through superlattice barriers is observed in a series of modulation doped AlGaAs heterostructures containing a superlattice within a parabolic potential. Due to occupation of a large fraction of the miniband, the resonance frequency decreases strongly with increasing superlattice barrier thickness.

Atmospheric and low pressure shadow masked MOVPE growth of InGaAs(P)/InP and (In)GaAs/(Al)GaAs heterostructures and quantum wells

The shadow masked growth technique is presented as a tool to achieve thickness and bandgap variations laterally over the substrate during metalorganic vapor phase epitaxy. Lateral thickness and bandgap variations are very important for the fabrication of photonic integrated circuits, where several passive and active optical components need to be integrated on the same substrate. Several aspects of the shadow masked growth are characterized for InP based materials as well as for GaAs based materials. Thickness reductions are studied as a function of the mask dimensions, the reactor pressure, the orientation of the masked channels and the undercutting of the mask. The thickness reduction is strongly influenced by the mask dimensions and the reactor pressure, while the influence of the orientation of the channels and the amount of undercutting is only significant for narrow mask windows. During shadow masked growth, there are not only thickness variations but also compositional variations. Therefore, we studied the changes in In/Ga and As/P ratios for InGaAs and InGaAsP layers. It appears that mainly the In/Ga-ratio is responsible for compositional changes and that the As/P-ratio remains unchanged during shadow masked growth.

Enhancement of photoluminescence from DX centers in AlGaAs heterostructures

Selectively excited room-temperature photoluminescence spectra of InGaAs-GaAs-AlGaAs quantum well heterostructures reveal a broad line at midgap energies originating in the Si doped AlGaAs. When carriers are photoexcited directly in the wells, this line is dramatically enhanced at the expense of the quantum well line, indicating carriers escape from the wells. The broad emission and its enhancement can be explained in terms of recombination between electrons trapped at DX centers in AlGaAs and holes transferred into AlGaAs from the neighboring wells. We also observe the broad emission by direct over-the-gap photoexcitation of very highly doped Si:AlGaAs. The doping dependence consistently correlates this line to DX centers.

An overview of visible light emitting diode (LED) development and the potential for AlInGaP devices

Recent developments in light-emitting diode (LED) materials growth and device properties are considered. The brightness of LEDs has increased in recent years, permitting new applications. Double heterostructure AlGaAs red LEDs on transparent 'substrates' are now commercially available for outdoor displays and signaling applications. Recently, AlInGaP LEDs grown by metalorganic chemical vapor disposition (MOCVD) have exhibited record performance in the yellow and red-orange spectral regions. External quantum efficiencies of greater than 5% and luminous performance as high as 20 lm/W at 590 nm have been reported. This performance is higher than that of conventional incandescent bulbs.

Dopant-induced disordering of annealed AlGaAs heterostructures

Impurity-induced layer disordering, i.e., outdiffusion of dopant and matrix elements, has been observed in superlattices and quantum wells. In this letter, we report on disordering in AlGaAs heterostructures in which only the central region of 650-Å-thick AlGaAs layers is Si doped. Disordering is clearly shown to be dependent on Si concentration and outdiffusion.

Matching of electronic wavefunctions and envelope functions at GaAs/AlAs interfaces

A method to calculate electronic wavefunctions and energies in AlGaAs heterostructures is developed and applied to some typical configurations. The method is based on the use of empirical pseudopotentials and the applicability of the flat-band approximation. Coupling of Gamma - and X-like conduction-band electrons is explicitly dealt with. Emphasis is put on the precise matching of wavefunctions at interfaces as well as on the connection rules for the related envelope functions. Among other things, the authors do not find evidence for boundary conditions for derivatives of envelope functions involving effective mass ratios.

Milliampere-range 'twice-buried' AlGaAs-heterolasers fabricated by low-temperature liquid phase epitaxy

The authors report on low-threshold quantum-well AlGaAs heterolasers emitting at wavelengths of 730-850 nm. A special LPE (liquid-phase epitaxy) technique has been developed to crystallize thin layer AlGaAs heterostructures in the low-temperature range of 400-600 degrees C. Values of threshold current density as low as 120 A/cm/sup 2/ at emitting wavelength lambda =845 nm and 380 A/cm/sup 2/ at lambda =760 nm were measured for wide-stripe geometry separate confinement lasers with 15-nm-thick active layers. 'Twice-buried' stripe laser heterostructures were developed to considerably narrow the width of the current channel, to confine the optical mode in lateral directions, and to compensate for the strain tensions in the active layer in order to solve the laser lifetime problem. Threshold currents as low as 2 mA at lambda =845 nm and 10 mA at lambda =765 nm were measured for 'twice-buried' stripe lasers without reflecting coatings on the facets (CW; T=300 K). The estimated lifetime was over 20000 h at room temperature.

Injection level controlled absorption on AlGaAs heterostructures

Injection level controlled absorption on AlGaAs heterostructures

Secondary ion mass spectrometry of dopants and impurities in compound semiconductors: Depth profiling of homo- and heterostructure

SIMS has been very successfully applied to the analysis of semiconductor materials. This paper presents some important results concerning the problems of III-V compound epitaxial layers: (i) high-purity GaAs epitaxial layer characterisation, (ii) the study of Si δ-doped GaAs in a AlGaAs heterostructure, (iii) parasitic As contamination of InP buffer layer in optoelectronic materials, (iv) crystal perfection and the highest allowed Si and Fe doping level in InP. Chemical and crystal quality analyses are often carried out on the same sample for a better assessment of the electronic material.

Localization in GaAs electron-dots and anti-dots

On GaAsAlGaAs heterostructures we have prepared a two-dimensionally modulated electron gas as well as arrays of quantum dots and anti-dots. In the far-infrared response quantum dots show the typical two-mode behavior characteristic for electron systems confined in all spatial dimensions under the influence of a magnetic field. The upper of these modes can also be observed in anti-dot arrays which indicates that localization takes place in magnetic fields in these systems, too. In transport measurements on anti-dots we observe a magnetoresistance maximum at low magnetic fields. It is interpreted as due to reduced diffusion in the superlattice when the cyclotron diameter matches the grating constant of the anti-dot array.

Carrier-induced blue shift of luminescence spectra from a 2-dimensional electron gas

We report on photoluminescence studies on a high mobility 2-dimensional electron gas (2DEG) in a GaAs AlGaAs heterostructure. We observe an intense recombination line which originates from the 2DEG. By applying a semi-transparent Schottky gate we prove that the line originates form the 2DEG. The intensity can be changed by varying the electron density between 0 and 7·10 11 cm −2. We observe a blue shift of the recombination line induced by photocarriers. The blue shift is about 10 meV for an excitation density of 1 W/cm 2. It is related to electrostatic effects due to built-up of photogenerated carriers causing bandstructure modifications. In particular, a shallow confinement potential for the holes occurs. From the strong temperature dependence of the luminescence around 10 K, the depth is estimated to be 1.5 meV.

Electron transport through single and multiple quantum dots: The formation of a one-dimensional bandstructure

We describe transport experiments performed on ballistic submicron devices which are defined in the two dimensional electron gas of GaAs AlGaAs heterostructures by means of metallic gates. Conductance measurements on single quantum dots reveal the formation of magnetically induced zero-dimensional (0D) states. In an array of 15 coupled quantum dots, these 0D-states develop into a 1D bandstructure.

High frequency properties and conductance of [formula omitted] microstructures

Fluctuations of the conductance, microwave photoconductance and photovoltage in mesoscopic GaAs AlGaAs heterostructures are studied. It is observed that their behaviour in a strong magnetic field (ω cτ ⪢ 1) is quite different for quasi two-dimensional and quasi one-dimensional devices.

Effects of etching with a mixture of HCl gas and H2 on the GaAs surface cleaning in molecular-beam epitaxy

I n situ cleaning of GaAs substrates with a HCl gas and hydrogen mixture prior to molecular-beam epitaxy has been investigated. The chemical reaction during etching was monitored using a quadrupole mass spectrometer. After etching, reflection high-energy electron diffraction patterns revealed (2×4) arsenic-stabilized surfaces and (4×2) gallium-stabilized surfaces as reconstructed structures in the gas-etched substrate surface. These structures suggest that the gas-etched substrate surface is atomically flat, resembling an epitaxial layer surface. To study the effect of gas etching, the carrier depletion layer and the residual carbon impurity around the substrate epitaxial interface were measured by capacitance-voltage carrier profiling and secondary-ion mass spectroscopy. After gas etching, the carrier depletion was greatly reduced, from 1.2×1012 to 1×1010 cm−2. The carbon impurity around the interface also decreased by one order of magnitude. We discussed the surface-cleaning mechanism using the atomic hydrogen terminating model of the GaAs surface during etching. We then applied this etching technique to in situ cleaning of semi-insulating GaAs substrates prior to the growth of selectively doped GaAs/N-AlGaAs heterostructures with very thin GaAs buffer layers.

Hole and electron traps in AlGaAs single and double heterojunction red light-emitting diodes

ABSTRACT Single and double heterostructure AlGaAs red LEDs, p+–N and n+–P AlGaAs-GaAs heterodiodes have been fabricated by liquid phase epitaxy (LPE). The presence and characteristics of deep centres located near the injection-active boundaries has been studied. Capacitance-temperature, electroluminescence, photocurrent and deep-level transient spectroscopy (DLTS) measurement have been performed. In n+–P structures a new Zn-related deep hole majority trap, at about 0·3 eV above the valence band, was found. In all p+–N heterojunctions, in addition to a majority electron trap related to the Te-dopant (DX defects), some acceptor-like traps have been detected.

Low-loss AlGaAs optical rectangular waveguides at 830 nm

Optical channel waveguides with rectangular cross section and losses less than 0.1 dB/cm at 830 nm have been fabricated in AlGaAs heterostructures grown by organometallic vapor phase epitaxy. The modal attenuation correlates with surface morphology for all waveguide widths and with sidewall roughness for narrow channels. Surface morphology and modal attenuation improve when a superlattice buffer layer is incorporated into the structure. The loss is also reduced when the arsenic source (arsine) is purified in-line.

Valley selective tunneling transistor based on valley discontinuities in AlGaAs heterostructures

The conduction-band discontinuities in AlxGa1−xAs/AlyGa1−yAs heterostructure for various valleys (Γ, L, X) are utilized to conceive of a valley selective tunneling transistor. At low temperature, the perpendicular tunneling current is very small because of the large Γ-Γ discontinuity and the small prefactor for Γ to X tunneling. However, if the valley population is altered by applying a lateral bias to the emitter, one can dramatically alter the perpendicular current since the X-X discontinuity is nonexistent and the L-L discontinuity is very small. By choosing proper values of x and y in the heterostructure, a very large current (power) change can be produced in the on and off states.

Minority carrier lifetime and efficiency in single heterostructure AlGaAs red light emitting diodes

Single heterostructure AlGaAs red LEDs fabricated by LPE have been characterized by applying electroluminescence, transient capacitance (DLTS), and minority carrier lifetime techniques. Temperature effects of band-to-band and band-to-acceptor radiative recombinations on integral efficiency and minority carrier lifetime have been analysed. A maximum in the integral efficiency is observed at the temperature where the peak amplitudes of the two emissions in the active layer are equal. Effective minority carrier lifetimes in the 150–300 K temperature range follow the temperature dependence of the radiative recombination coefficient and an internal quantum efficiency close to unity is obtained. Between 70 and 150 K, some samples present two different consecutive time constants from which an activation energy of 50 meV for the acceptor level in the Zn-doped active layer was calculated. Measured deep levels do not present any significant influence on either internal efficiency or minority carrier lifetime.