Alx Ga1 Research Articles

Electrical properties of Be+ ion-implanted Alx Ga1−xAs p-n junctions

Electrical properties of Be+ ion-implanted Alx Ga1−xAs p-n junctions

Miniband dispersion in GaAs/AlxGa1−xAs superlattices with wide wells and very thin barriers

Photoreflectance spectra have been used to characterize miniband formation in GaAs/ Alx Ga1−x As superlattices with wide wells (275–255 Å) and withb arriers as thin as 17 Å. Thirty-two optical transitions are resolved in the photoreflectance spectra of the 17 Å barrier sample. These experimental transitions match all those theoretically predicted from the selection rule Δn=0, including Γ- and Π-type transitions arising from miniband dispersion; these results imply sample perfection. A sample with a 40 Å barrier exhibits forbidden transitions with Δn≠0; these additional transitions, together with the narrow width of the minibands for 40 Å barriers, create difficulty in resolving the miniband structure.

The role of aluminum in selective reactive ion etching of GaAs on AlGaAs

We have studied the role of aluminum in the formation of an etch barrier at the GaAs/ Alx Ga1−x As interface during reactive ion etching in CCl2 F2 plasma. The minimum Alx Ga1−x As thickness needed to form the barrier is Al mole fraction dependent and was determined with etching experiments monitored by optical emission spectroscopy. Effective Alx Ga1−x As layers for forming an etch barrier are 275 Å for x=0.02, 22 Å for x=0.10, 15 Å for x=0.15, 12 Å for x=0.20, and 9 Å for x=0.30. For all Al mole fractions except x=0.02, these thicknesses correspond to a sheet dose equivalent to 3/4 of a monolayer of Al in the original Alx Ga1−x As layer. Barrier layers for x=0.02, 0.10, 0.25, and 0.30 were examined without air exposure by angle-dependent x-ray photoelectron spectroscopy. For samples that are not overetched, the surface is covered with ∼20 Å of AlF3 intermixed with a gallium halide containing chlorine and fluorine and is depleted of arsenic. For substantially overetched barriers, a 30 Å layer is formed with gallium halide present at the surface, AlF3 found farther in, and arsenic depletion throughout the barrier. During extreme overetch, barrier layers on the order of tens of Å in thickness were not etched away and yet did not completely prevent very slow etching of underlying GaAs. Barrier layers on the order of 60 Å in thickness did prevent etching of underlying GaAs. Collectively the data suggest that the role of Al is formation of AlF3 exclusively and that only this compound is responsible for stopping the GaAs etch.

Self-consistent calculations of tunneling currents in n+-GaAs/i- AlxGa1−xAs/n+-GaAs structures and comparison with measurements

We present calculations and measurements of current as a function of voltage I(V), and conductivity at low voltage as a function of temperature, G(T), for n+ -GaAs/i- Alx Ga1−x As/n+ -GaAs single-barrier tunneling structures. The current is modeled by its tunneling and thermionic emission components. The shape of the conduction-band edge is obtained by solving Poisson’s equation self-consistently, together with two different models for the charge density. In the first model, the electron density is evaluated semiclassically, and in the second, the electron density is calculated from the electronic wave functions. Good agreement is obtained with both models between the experimental and the calculated I(V) and G(T) characteristics over the 4.2–200 K temperature range. The fits obtained are very sensitive to small variations (1%) in barrier width and effective barrier height, which allows one to determine these parameters within a narrower uncertainty range.

D X-center-like traps and persistent photoconductivity in Te-doped AlxGa1−xSb on GaSb

The donor-related deep electron traps in Te-doped Alx Ga1−x Sb on GaSb substrate were investigated by deep level transient spectroscopy, capacitance-voltage, photocapacitance, and Hall-effect measurements. Deep electron traps were not detected in the Al composition range 0≤x<0.2, but were detected in the higher range of x. The concentration of the deep electron traps increases steeply with x and then saturates. The concentration also increases linearly with donor concentration for the same Al composition. In the temperature-dependent Hall-effect measurement, both shallow donor and deep donor levels were observed. The deep donor is dominant for x≥0.4, and the thermal activation energy E0 increases dramatically from 6 to 110 meV in the range of 0.2<x≤0.5. Persistent photoconductivity was observed for x≥0.3 at temperatures below 100 K. All the experimental results indicate that the deep electron traps in Te-doped Alx Ga1−x Sb are quite similar to the DX center in Alx Ga1−x As.

Diffuse scattering and superstructure reflections from In1−y(AlxGa1−x)yP

The structure of In1−y (Alx Ga1−x )y P semiconductor alloy systems was studied by electron diffraction. Varied distribution of diffuse scattering and superstructure reflections was observed. The pertinent ordered structure is dependent on growth parameters, but not on the alloy systems. The diffuse scattering could be attributed to mean square atomic displacements due to the coexistence of different column III atoms in the same sublattice.

Optimisation of four-and five-layer Alx Ga1−x As/GaAs large optical cavity lasers for high power, low threshold current density operation

Optimisation of four-and five-layer Alx Ga1−x As/GaAs large optical cavity lasers for high power, low threshold current density operation

Molecular beam epitaxy of GaSb0.5As0.5 and AlxGa1−xSbyAs1−y lattice matched to InP

Single crystal films of GaSby As1−y and Alx Ga1−x Sby As1−y alloys having compositions within the miscibility gap can be prepared using nonequilibrium growth techniques. We have successfully grown these alloys lattice matched to InP by molecular beam epitaxy. Transmission electron microscopy studies of these alloys grown on (100) InP at 500–560 °C show evidence of compositional modulation due to spinodal decomposition similar to that of InGaAsP grown by vapor phase epitaxy on InP used for laser diodes emitting at ∼1.5 μm. From the studies of optical microscopy, x-ray diffraction, and photoluminescence measurements at both room temperature and liquid helium temperature, these epitaxial layers are considered of high quality for optoelectronic device applications in the wavelength range of 0.65–1.7 μm lattice matched to InP substrates.

Accurate electron probe determination of aluminum composition in (Al, Ga)As and correlation with the photoluminescence peak

The composition of Alx Ga1−xAs has been measured with improved accuracy by electron probe microanalysis using an aluminum-copper alloy standard rather than an elemental aluminum standard. Details of the experimental procedure are given. A calibration curve, relating the photoluminescence peak energy (Ep) to aluminum concentration (x), has been obtained. A least-squares fit to the data gives Ep(eV)=1.42+1.45x−0.25x2 for 0<x≤0.45.

Simulation of near ballistic electron transport in a submicron GaAs diode with ALx Ga1−x As/GaAs heterojunction cathode

A Monte-Carlo simulation program has been developed to simulate the motion of electrons in a submicron GaAs diode with an AlxGa1−xAs/GaAs heterojunction cathode. The electric field in the diode is self-consistently determined by solving Poisson's equation under reasonable boundary conditions. The distributions of electron energies and electron velocities, and the profiles of the electron density, electric field and average electron velocity, are computed. Based on these data, various properties of the electron transport in a submicron diode with a hot-electron injection mechanism are discussed.

Optical properties of iron doped AlxGa1−xAs alloys

Photocapacitance measurements were used to study the photoionization cross-section spectra of holes in iron doped Alx Ga1−xAs. The spectra are well described by the crystal field theory giving a nearly constant crystal field splitting of about 0.36 eV for all compositions studied. As a result of an extended range of composition (0≤x≤0.76), it was possible to show that the binding energy of the dominant iron center increases linearly with composition and that the relative position of the center is not related to any of the conduction band minima. The variation of the energy for Γ1(5E)→Γ5(5T2) transition in Fe2+(3d6) is discussed for different host crystals.

Broadband tuning (ΔE∼100 meV) of Alx Ga1−xAs quantum well heterostructure lasers with an external grating

Alx Ga1−xAs-GaAs quantum well heterostructure laser diodes are shown to be tunable over a 100-meV range when operated continuously (cw) at room temperature in an external cavity with a grating to control feedback. The gain profile of the n=1 and n′=1′ (electron-to-heavy hole and electron-to-light hole, e→hh and e→lh) transitions and the n=2 electron-to-heavy hole transitions are clearly outlined by the intensity profile of the selected laser lines. The partial homogeneous broadening of the gain profile agrees with rapid carrier relaxation in the well. The diodes contain a single 60–90-Å GaAs well and are grown by metalorganic chemical vapor deposition.

Superlattices from mismatched materials

Leo Esaki and Raphael Tsu at IBM pointed out in 1970 that imposing an artificial periodicity one or two orders of magnitude larger than the natural lattice spacing on a semiconductor crystal ought to yield novel and potentially useful electrical and optical effects. Since then, considerable work has been done on fabricating and investigating the properties of superlattices—epitaxially grown stacks of alternating thin layers (on the order of a hundred angstroms) of two different semiconductor materials. But until recently the requirement of good, defect‐free crystal matching at the interfaces has severely restricted the choice of materials used to grow such artificially periodic structures. Almost all superlattices were grown with alternating layers of GaAs and Alx Ga1−x As with the lattice constants (spacings) of the two materials differing by only about a part in a thousand.

Picosecond AlxGa1−xAs modulation-doped optical field-effect transistor sampling gate

New modulation-doped Alx Ga1−xAs/GaAs metal-semiconductor field-effect photodetectors have been fabricated and tested in a novel picosecond optical sampling gate configuration. The rise time was measured to be 12 ps, with a full width at half-maximum of 27 ps. The optical electronic picosecond cross-correlation measurement has shown the importance of the two-dimensional electron gas for high-speed operation.

Use of a superlattice to enhance the interface properties between two bulk heterolayers

Single interface modulation-doped Alx Ga1−xAs /GaAs heterostructures with the binary on top of ternary were grown by molecular beam epitaxy. By incorporating a 150-Å-thick Alx Ga1−xAs /GaAs three-period superlattice in place of an undoped Alx Ga1−xAs spacer layer, 10-K mobilities of up to 256 000 cm2/Vs were obtained. This value is about 6.5 times that of the previous best value. This dramatic improvement is tentatively attributed to the relief of strain caused by the small but significant lattice mismatch although impurity trapping by the superlattice may also play a role. Normal modulation-doped structures where the ternary is grown on top of binary also showed mobility improvement (about 30%) when the undoped AlGaAs spacer layer is replaced with a three-period superlattice of the same thickness. This concept should have a significant role in heterojunction bipolar transistors, field-effect transistors, lasers, and other heterojunction devices.

The growth of high quality Alx Ga1−xAs by molecular beam epitaxy and its application to double-heterojunction lasers

The molecular beam epitaxial (MBE) growth of high quality Si‐doped (n‐type) and Be‐doped (p‐type) Alx Ga1−xAs with 0<x<0.4 is reported. Room temperature mobilities and radiative recombination efficiencies comparable to those of high quality liquid phase epitaxial (LPE) and organometallic vapor phase epitaxial (OMVPE) material have been obtained. MBE grown double‐heterojunction lasers with Al0.07 Ga0.93As active layers have been fabricated. Broad area lasers having threshold current densities between 880 and 1000 A/cm2 and narrow stripe lasers having threshold currents as low as 84 mA are reported. These values are comparable to the best results for LPE and OMVPE lasers with similar structures.

Transfer doping effects at the organometallic vapor phase epitaxial AlxGa1−xAs-substrate GaAs interface

Electron mobilities in Alx Ga1−xAs (0.1≤x≤0.6) crystals grown by organometallic vapor phase epitaxy on semi-insulating GaAs:Cr have been measured and analyzed. The mobilities are an order of magnitude higher than theoretical predictions, or those obtained in liquid phase epitaxial Alx Ga1−xAs for x≥0.4. The expected lower mobilities are, however, obtained when measurements are made on the epitaxial layer with the substrate removed. A persistent photoconductivity effect is observed at low temperatures in the layers with substrates. The present results indicate that transfer doping is operative at the epilayer-substrate heterointerface.

Mg+ implantation into AlxGa1−xAs

Ion implantation of Mg into Alx Ga1−xAs was carried out at room temperature. After annealing at 700 °C, GaAs showed nearly 100% electrical activation, however, Al0.60Ga0.40As showed only 15% electrical activation. We explain this result in terms of increasing acceptor energy level and outdiffusion of Mg with increasing alloy composition x.

Experimental and theoretical electron mobility of modulation doped AlxGa1−xAs/GaAs heterostructures grown by molecular beam epitaxy

Single period modulation doped Alx Ga1−x As/GaAs heterostructures have been grown by MBE and characterized. The incorporation of a thin undoped Alx Ga1−x As layer between the doped Alx Ga1−x As and undoped GaAs layers further improves the electron mobility through the reduction of remote donor scattering. Electron mobilities as high as 8165, 80 900, and 115 000 cm2 V−1 s−1 at 300, 78, and 10 K respectively, for an average sheet electron concentration of 5×1011 cm−2 were obtained. The best mobility was obtained when the undoped Alx Ga1−x As layer thickness was 75 Å for both x = 0.25 and x = 0.33. These figures represent the best mobilities associated with single period Alx Ga1−x As/GaAs structures reported to date. Good agreement between the experiments and mobility calculations have also been obtained. The theory is based on heavily screened remote impurity scattering and quasi-two-dimensional electron-phonon interaction.

Lattice constants in the Alx Ga1−x Sb system

physica status solidi (a)Volume 61, Issue 1 p. K51-K53 Short Note Lattice constants in the Alx Ga1−x Sb system H. Sonomura, H. Sonomura College of Engineering, University of Osaka Prefecture Search for more papers by this authorT. Nishimura, T. Nishimura College of Engineering, University of Osaka Prefecture Search for more papers by this authorT. Miyauchi, T. Miyauchi College of Engineering, University of Osaka Prefecture Search for more papers by this author H. Sonomura, H. Sonomura College of Engineering, University of Osaka Prefecture Search for more papers by this authorT. Nishimura, T. Nishimura College of Engineering, University of Osaka Prefecture Search for more papers by this authorT. Miyauchi, T. Miyauchi College of Engineering, University of Osaka Prefecture Search for more papers by this author First published: 16 September 1980 https://doi.org/10.1002/pssa.2210610152Citations: 8 Sakai, Osaka 591, Japan. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume61, Issue116 September 1980Pages K51-K53 RelatedInformation