Search

Surface photovoltage (SPV) spectra were measured for GaN 0.014 As 0.986 layers at room temperature and compared with room temperature photoreflectance (PR) and contactless electroreflectance (CER) measurements. Spectral features related to E − and E + transitions were clearly observed in SPV spectra at energies corresponding to PR and CER resonances. In this way it has been shown that SPV spectroscopy is an alternative absorption-like technique to study both the E − and E + transitions in dilute nitrides. The observation of E + transition in SPV spectra means that it is a direct optical transition at the Γ point of GaNAs band structure which can be explained by the band anticrossing interaction between the localized states of N and the extended conduction band states of the GaAs host.

We report the formation of CdTe self-assembled quantum dots (QDs) on high-quality ZnTe epilayers grown on a GaSb substrate by molecular-beam epitaxy. Reflection high-energy electron diffraction and atomic force micro- scopy measurements clearly show the formation of CdTe QDs. Photoluminescence (PL) measurements on ZnTe-capped CdTe QD samples show a wide distribution of dot size. The temperature dependence of PL spectra indicates much stronger exciton localization in QDs than that in quantum wells.

AlInAs microdisk cavities having quality factor Q ~ 15 000 were fabricated from lattice-matched InP/AlInAs (interface/aggregation) quantum dot (QD) structures using wet chemical etching. The QD emission coupled to whispering gallery modes was observed at spectral range 920 - 1000 nm at temperatures of 10 - 160 K. The laser generation with threshold power density of 50 W/cm2 at T = 10 K was observed under optical pumping. It was found that the spontaneous emission coupling factor β equals 0.23 for these microdisks. The low temperature lasing operation and the small coupling factors observed suggest the existence of small QDs formed at the InP/InAlAs interface as the main active elements.

InGaN quantum dot (QD) formation in a wide pressure range MOCVD reactor was studied. The existence of QDs and their lateral size (2–5 nm) were demonstrated using transmission electron microscopy and high spatial resolution (~ 100 nm) near-field magneto-photoluminescence spectroscopy. We found that an increase of the reactor pressure from 400 to 1000 mbar leads to an order of magnitude increase in light emission efficiency of the InGaN / GaN QDs accompanied by ~ 100 meV redshift of the emission wavelength. We explored stimulated phase separation (SPS) to control carrier localization and emission wavelength. The SPS was achieved by adding In in the matrix material. This leads to formation of extremely deep InGaN / InGaN QDs having energy localization up to ~ 0.8 eV, which was revealed from selectively excited far-field photoluminescence (PL) spectra. Without SPS the QD activation energy is found to be below 0.2 eV. A nonequilibrium carrier population strongly suppresses the temperature-induced shift of the PL emission in deep InGaN QDs.

We report the characteristics of InP self-assembled quantum dots embedded in In0.5Al0.5P on GaAs substrates grown by metalorganic chemical vapor deposition. The InP quantum dots show increased average dot sizes and decreased dot densities, as the growth temperature increases from 475°C to 600°C with constant growth time. Above the growth temperature of 600°C, however, dramatically smaller and densely distributed self-assembled InP quantum dots are formed. The small InP quantum dots grown at 650°C are dislocation-free “coherent” regions with an average size of ∼20 nm (height) and a density of ∼1.5 × 108 mm−2. These InP quantum dots have a broad range of luminescence corresponding to red or organge in the visible spectrum.

An introduction to the operation of quantum-dot cellular automata (QCA) is presented, along with recent experimental results. QCA is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two electrometers. The dots are metal islands, which are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. A noninvasive electrometer is presented which improves the sensitivity and linearity of dot potential measurements. The operation of this basic cell is confirmed by an externally controlled polarization change of the cell.

We present experimental demonstration of a basic cell of Quantum-dot Cellular Automata, a transistorless computation paradigm which addresses the issues of device density and interconnection. The devices presented consist of four and six-dot quantum-dot cellular systems where the metal dots are connected by capacitors and tunnel junctions. The operation of a basic cell is confirmed by the externally controlled polarization change of the cell. The cell exhibits a bistable response and voltage gain. We present an experimental technique which cancels the parasitic cross-talk capacitors in the system.

We discuss the formation of self-assembling II–VI quantum dots during MBE growth, with emphasis on CdSe dots grown on ZnSe. AFM measurements on specimens with uncapped dots show relatively narrow dot size distributions, with typical dot diameters of 35 ± 5nm. Uncapped CdSe dots are unstable with time, showing clear evidence of ripening. Photoluminescence from capped dots indicates strong exciton localization, as evidenced by very intense PL emission even at relatively high temperatures.

The emission spectrum of self-assembled InGaAs/GaAs quantum dots filled with up to 10 excitions is measured in magnetic fields up to 13 Tesla. The spectrum shows a number of peaks which split and rearrange with the magnetic field. The behaviour of the spectrum with carrier density and magnetic field is compared with detailed calculations. The model allows us to interpret our results in terms of coherent many-exciton states and their destruction by the magnetic field. The level structure of the spectra is related to the shell structure and collective excitations of many-excition droplets in these artificial atoms.

We present selective photoluminescence and photoluminescence excitation spectroscopy on self-assembled quantum dots. These spectroscopic techniques reveal a large apparent `Stokes' shift in In(Ga)As-Ga(Al)As self-assembled quantum dots. We demonstrate that the first two excited states observed in PLE originate from the doubly-degenerate first excited state. The ground state is not observed in the quantum dot PLE due to the sharp d-funtion-like density of states of individual dots. Our experimental data agree with a recent theoretical calculation, suggesting that both the degeneracy-lifting and broadening of energy levels are caused by the random potential of compositional, size and strain fluctuations. Due to large energy separations in these quantum dots, we also demonstrate the importance of multi-phonon relaxation processes

Several practical issues in the development and operation of quantum-dot cellular automata (QCA) cells and systems are discussed. The need for adiabatic clocking of QCA systems and modeling of electrostatic confinement of quantum dots are presented. Experimental data on dot coupling and applications to QCA detectors in a 2-dimensional electron gas (2DEG) are presented. We report a charge detection scheme where we observe strong modulation in the detector signal, in addition to the detector exhibiting minimal effect on the dot being measured. With this investigation, we demonstrate these two key components required for QCA in AlGaAs/GaAs materials, namely dot coupling and charge-state detection.

Near-surface GaAs AlGaAs quantum wells, with and without a GaAs cap, have been used as effective probes of the electronic properties of oxidized GaAs surfaces and AlGaAs surfaces. We find that the variation of surface stoichiometry due to hydrogen ion treatments appears to be similar for both oxidized AlGaAs and GaAs surfaces, as examined by Auger electron spectroscopy. However, the composition of the oxide significantly affects both hydrogenation process and the efficacy of surface passivation.

We investigated impurity-induced disordering (IID) in AIGalnAs multi-quantum wells (MQWs) on InP substrate by Zn diffusion under low temperature conditions. Blue-shift of band-gap energy of lattice-matched AIGalnAs MQW on InP strongly depended on the temperature of Zn diffusion. The lattice-matched MQW was not completely disordered below 500°C. On the other hand, photoluminescence spectra from compressively strained AIGalnAs MQW, after disordering was independent of the temperature of Zn diffusion. Considerable disordering was observed in the strained MQW, which was saturated even at the low temperature of 400°C. The measured hole concentration of the Zn diffused layer at 400°C was as low as 3 × l018cm−3 The IID lasers were also fabricated and characterized. No significant increase in the optical loss due to the Zn diffusion was observed in these lasers.

Correlation between particles in finite quantum systems leads to a complex behavior and novel states of matter. One remarkable example of such a correlated system is expected to occur in an electron gas confined in a quantum dot (QD), where at vanishing electron density the Coulomb interaction between electrons rigidly fixes their relative positions like those of the nuclei in a molecule. Unlike real molecules, however, which have sizes and properties fixed by their chemical constituents, the size, shape and electronic density of such confined electronic structures, referred to as Wigner molecules (WM), can be varied experimentally using various combinations of semiconductor materials, types of nanostructures, numbers of electrons, electrostatic potentials and magnetic fields. Thus these WMs present a novel and compelling field for fundamental and applied research. So far, however, the properties of WMs and their underlying fundamental physics have been studied primarily by theory; what little experimental evidence there is for their existence consists only of measurements of charging energies and light-scattering spectra of GaAs/AlGaAs quantum dots created from modulation doped 2D-electron gas heterostructures.

The exciton bound to the shallow Si-donor confined in a 100A wide GaAs quantum well has been studied in selective photoluminescence (SPL) and photoluminescence excitation (PLE) spectroscopy. The transition from the ground state, ls(Γ6), to the first excited state, 2s(Γ6), of the confined Si donor has been observed via two-electron transitions (TETs) of the donor bound exciton observed in SPL for the first time to the best of our knowledge. The interpretation of the TET peaks is confirmed by PLE measurements. Further, from Zeeman measurements, the magnetic field dependence of the donor ls(Γ6)-2s(Γ6) transition energy has been determined.

We report the first confirmation of disordering of ZnSe/ZnS strained layer superlattices (SLSs) by Ge diffusion. The as-grown sample showed ±first orders of well-resolved double crystal x-ray satellite peaks due to SLS periodic structure. However, the satellite peaks completely disappeared in the Ge-diffused sample, indicating that the SLS structure was disordered by the Ge diffusion. Photoluminescence measurements at 1.4K of both the as-grown and the annealed samples without Ge diffusion show identical, sharp excitonic emission around 420 nm. After Ge diffusion, the PL peaks shift to higher energy confirming the layer disordering of the SLS.

The exciton bound (BE) at the shallow Be acceptor confined in a narrow GaAs/AlGaAs quantum well (QW) has been investigated by means of selective photoluminescence (SPL) and PL excitation (PLE) experiments. For the shallow acceptor, several excited states have been observed as two-hole transition (THT) satellites of the BE. The heavy hole (hh)-like excited nS(Γ 6 ) acceptor states dominate the satellite spectrum, but also the light hole (lh)-like excited 2S(Γ 7 ) and the parity forbidden transition to the 2P 3/2 excited state have been monitored in SPL spectra. When detecting a THT satellite, the 1S(Γ 7 ) hh-like acceptor ground state has been spectrally resolved from the 1S(Γ 6 ) hh-like state in PLE spectra. Several BE states have been theoretically predicted and observed in PLE spectra with the J=5/2 state at lowest energy, like in bulk GaAs. The proposed interpretation of the acceptor hh- and 1h-states is confirmed by SPL and PLE experiments in the presence of an applied magnetic field and in polarized PLE measurements. An effective g-value for the acceptor BE recombination in varying degree of confinement is derived from these Zeeman measurements

We report low-temperature studies of microwave-induced cyclotron resonance of photo-generated carriers in (A1,Ga)As serpentine superlattice quantum-wire arrays. The geometric size of the parabolic-crescent cross-section of the quantum wires was of the order of 100 A x 50 A, depending on the angle of the vicinal substrate and the amount of parabolic curvature. Comparing the obtained spectra, we estimate the relative degree of carrier confinement in the ordered AlGaAs structure.

Top-driven lasers have been fabricated by impurity-induced disordering (IID). Compared with conventional top-driven lasers, that is, transverse-junction-stripe (TJS) lasers, the top-driven IID (TID) lasers are unique in that the carriers in the active quantum-well stripe, are injected vertically from (instead of laterally between) the cladding layers of the lasers. Because vertical injection is much more efficient than lateral injection, the threshold current of the TID lasers is lower than that of TJS lasers by a factor of 2-10. The lowest threshold current observed for the TID lasers was 1.6 mA under room-temperature continuous-wave (CW) operation. By using proper material design and device processing, the top n-type contact of the TID lasers obtained is virtually as good as the bottom n-type contact of conventional IID lasers. >

We have investigated the influence of Si-N complexes on the electronic properties of GaAsN alloys. The presence of Si-N complexes is suggested by a decrease in carrier concentration, n, with increasing N-composition, observed in GaAsN: Si films but not in modulation-doped heterostructures. In addition, for GaAsN: Te (GaAsN:Si), n increases substantially (minimally) with annealing-T, suggesting a competition between annealing-induced Si-N complex formation and a reduced concentration of N-related traps. Since Si-N complex formation is enhanced for GaAsN: Si growth with the (2x4) reconstruction, which has limited group V sites for As-N exchange, the (Si-N)(As) interstitial pair is identified as the dominant Si-N complex. (C) 2009 American Institute of Physics. (DOI: 10.1063/1.3198207)

A minimally invasive laser-induced injury model is described to study thrombus development in mice in vivo. The protocol involves focusing the beam of an argon-ion laser through a compound microscope on the vasculature of a mouse ear that is sufficiently thin such that blood flow can be visualized by intravital microscopy. Two distinct injury models have been established. The first involves direct laser illumination with a short, high-intensity pulse. In this case, thrombus formation is inhibited by the GPIIb/IIIa antagonist, G4120. However, the anticoagulants, hirulog, PPACK, and NapC2 have minimal effect. This indicates that thrombus development induced by this model mainly involves platelet interactions. The second model involves low-intensity laser illumination of mice injected with Rose Bengal dye to induce photochemical injury in the region of laser illumination. Thrombi generated by this latter procedure have a slower development and are inhibited by both anticoagulant and anti-platelet compounds.

We used near-field magneto-photoluminescence scanning microscopy to study structural and optical properties of quantum-dot-like compositional fluctuations in GaAsN and InGaAsN alloys. We show that these fluctuations manifest themselves by the appearance of narrow emission lines (halfwidth 0.5−2 meV) at temperatures below 70K. We estimated the size, density, and nitrogen excess of individual compositional fluctuations (clusters), revealing phaseseparation effects in the distribution of nitrogen in GaAsN and InGaAsN. We found a dramatic difference in the Zeeman splitting of cluster lines between GaAsN and InGaAsN, indicating a strong effect of In on the exciton g-factor.

We present the first radiative lifetime measurements and magneto-photoluminescence results of excited states in InGaAs/GaAs semiconductor self-assembled quantum dots. By increasing the photo-excitation intensity, excited state interband transitions up to n = 5 can be observed in the emission spectrum. The dynamics of the interband transitions and the inter-sublevel relaxation in these zero-dimensional energy levels lead to state-filling of the lower-energy states, allowing the quasi-Fermi level to be raised by more than 200 meV due to the combined large inter-sublevel spacing and the low density of states. The decay time of each energy level obtained under various excitation conditions is used to evaluate the inter-sublevel thermalization time. Finally, the emission spectrum of the dots filled with an average of about eight excitons is measured in magnetic fields up to 13 Tesla. The dependences of the spectrum as a function of carrier density and magnetic field are compared to calculations and interpreted in terms of coherent many-exciton states and their destruction by the magnetic field.

Selectively excited photoluminescence (SPL) of an array of self-organized In$_{0.5}$Ga$_{0.5}$As quantum dots has been measured in a magnetic field up to 11T. Anomalous magnetic field sensitivity of the SPL spectra has been observed under conditions for which the regular photoluminescence spectra is insensitive to the magnetic field due to large inhomogeneous broadening. The anomalous sensitivity is interpreted in terms of the repulsion of excited levels of the dots in a random potential. A theory presented to describe this phenomena is in excellent agreement with the experimental data. The data estimated the correlation in the positions of excited levels of the dots to be 94%. The magnetic field dependence allows the determination of the reduced cyclotron effective mass in a dot. For our sample we have obtained $m_em_h/(m_e+m_h)=0.034m_0$., Comment: 12 revtex preprint pages + 4 ps figures, uuencoded

The tunneling mechanism of electrons and holes to surface states from near‐surface Al0.3Ga0.7As/GaAs quantum wells has been investigated by steady‐state and time‐resolved photoluminescence spectroscopy, near liquid‐helium temperature, of the excitonic e1‐hh1 transition in the well. The ensemble of the data, taken over a wide range of optical excitation levels, for various values of the tunneling‐barrier thickness, and before and after passivation of the surface by hydrogen, allows a description both of the details of the tunneling mechanism and of the character and behavior of relevant surface states. The main results are summarized as follows: (i) steady‐state tunneling is ambipolar, namely, separate for electrons and holes, rather than excitonic; (ii) Spicer’s advanced unified defect model for an oxidized GaAs surface, antisite‐As donors as dominating surface traps, provides an appropriate description of the state distribution at the interface between AlGaAs and its oxide; (iii) hole accumulation in sur...

In this work, 10 and 20 nm diameter colloidal CdSe nanowires (NWs) have been successfully incorporated into ZnSe layers grown by molecular beam epitaxy on GaAs substrates. Atomic force microscopy and scanning electron microscopy were carried out to study the surface morphology of the samples. Transmission electron microscopy and energy-dispersive x-ray analysis were also carried out to study the chemical composition and lattice structure around the embedded CdSe NWs. Finally, single NW photoluminescence (PL) spectroscopy and PL imaging were used to study the optical properties of ZnSe films containing CdSe NWs. The experimental results confirm the presence of embedded CdSe NWs in the ZnSe films and show that the embedded NWs remain optically active.

The role of surface states in reducing the radiative efficiency of a GaAs/AlGaAs quantum well (QW), situated in proximity of the surface, has been investigated. The near-surface QW photoluminescence (PL) was utilized as a probe of the effects of room-temperature hydrogen irradiation and of the subsequent evolution of the system in time. The e1 - hh1 PL at 1.4 K of various near-surface wells, differing in distance from the surface, was found to drop when the AlGaAs barrier was made thinner than 150 angstroms, due to short-circuiting recombination processes at the surface. The data were interpreted in terms of electron and hole tunneling to surface states. A study of the stability of the passivation effect -- samples being investigated again after an eight-month-long exposure to air, or after annealing in vacuum -- is indicative of important changes in the lifetimes of the different radiative and non-radiative processes associated with the well.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

(Al,Ga)As serpentine superlattice (SSL) quantum-wire arrays with a paraboliccrescent cross section have been grown on vicinal GaAs substrates by molecular beam epitaxy. The quantum wires have dimensions on the order of 5 nm and 1D confined valence band states have been reported previously. Here we report on subsequent SSL samples having photoluminescence (PL) linewidths of 5 meV and displaying well-resolved excitation spectra. The data were obtained at 1.4 K and include linearly-polarized PL and PL excitation spectra (PLE) taken normal to the vicinal (100) surface. These data were fitted with effective-mass calculations that include the SSL geometry, valence band mixing, and imperfect lateral composition modulation. In linear polarized PLE (polarized parallel and perpendicular to the quantum wires), we have been able to resolve a SSL-induced heavy-light hole splitting of the ground state exciton. The observed heavy-light hole splitting is of the order of 5 meV with an electron-heavy hole subband separation of 15-20 meV. We extract a lateral composition modulation between the barrier and the wire to be 15 % from the observed heavy-light hole splitting corresponding to a lateral potential-energy difference in the conduction band of about 120 meV.

We used high spatial resolution near-field scanning optical microscopy (NSOM) to measure low-temperature (10K) emission spectra of single InP/GaInP QDs (lateral size ~100 nm) at magnetic fields up to 10 T. A multi-electronic structure having energy splitting 3–5 meV, resulting from charging of the dot up to 20 electrons, has been observed for these QDs. We measured a strong variation of the near-field emission intensity on a length scale ~30 nm related to Wigner localization. Magnetic-field-induced shifts of the multi-shell peaks for some dots follow remarkably well the energy levels of a Fock-Darwin Hamiltonian, which allow the observation of a Wigner-molecular-droplet transition.

Summary form only given. The authors report on strained InGaAs-QW impurity-induced disordering (IID) lasers having self-aligned structure with very low threshold current and moderate blue-shift of the lasing wavelength. The strained InGaAs-QW material employed was grown by MOCVD. The fabrication process is described. The authors believe that IID by Si diffusion is a very attractive approach for the fabrication of strained InGaAs-QW lasers. >

Summary form only given. A report is presented on the fabrication and measurement of ZnSe/GaAs heterostructure bipolar transistor (HBT) device structures. Using a wide-gap emitter allows increased design flexibility since it decouples constraints between the base doping and emitter injection efficiency. The ZnSe/GaAs interface is ideal since it provides a large barrier in the valence band for the holes, but only a small barrier in the conduction band for the electrons. This combination of band offsets guarantees the back injected base current will be small independently of the base doping. In addition, the lattice mismatch is small (0.27%). Combining II-VI/III-V materials opens up to a new class of device possibilities. Results are presented for the ZnSe/GaAs HBT device structures. Increased optimization of the structure and more mature processing technology should improve device characteristics further. >

Etched-pillar, bottom-emitting vertical cavity lasers have been fabricated using lateral oxidation of AlAs. The devices have threshold currents as low as 315 µA for a 4 µm × 4 µm, three quantum well active region. Using the data and a numerical model the authors extract excess optical and carrier losses and an effective surface recombination velocity for the devices. The data show that size dependent optical scattering persists as the lasers are scaled to smaller sizes, but lateral carrier leakage is suppressed, allowing for scaling of lasers to small sizes to achieve lower threshold currents.

The electrorefractive effect in a GaAs/AlGaAs superlattice was measured by using a monolithic Fabry-Perot structure, where the superlattice active region is embedded inside a cavity formed by two quarter-wave stacks, all grown by molecular beam epitaxy. At the wavelength ∼7675 A, there is a large absorption change (∼5400/cm) and an accompanying index change (∼0.015) when the applied field change is ∼100 kV/cm. In addition, the chirp parameter at this wavelength is less than 1. This result shows that superlattice electroabsorption optical modulators can offer relatively very low chirp

Stripe-geometry strained InGaAs-GaAs quantum well lasers were fabricated by impurity induced disordering. Threshold currents as low as 2.2 mA at room temperature continuous operation (RT CW) were obtained for uncoated lasers having 1.2 mu m wide, 215 mu m long active stripes. The authors believe that this ultralow threshold is mainly due to the very small active stripe width and the excellent electrical confinement of the laser.

A normally-on high-performance asymmetric Fabry–Perot modulator using the quantum confined Stark effect in GaAs quantum wells confined by short period AlAs–GaAs superlattices is reported. The modulator is the first of this type to exhibit simultaneously low insertion loss ( 68%) and practically infinite contrast at the Fabry–Perot resonance for an operating voltage swing of under 4 V.

This device consists of a five-layer transverse-junction-stripe laser structure monolithically integrated with an external three-layer waveguide. The transverse p-n junction within the laser cavity permits the use of a vertical p-n junction in the external waveguide for future implementation of a modulator without disturbing the laser operation. As a result, this structure allows for flexibility in the design of the external waveguide/modulator without resorting to complicated regrowth procedures. Design curves for two different types of optical cavities are presented, and the reflectivity and transmission of the etched facet as a function of active layer thickness is modeled in detail using an excitation field approach. Finally, integrated laser/waveguide devices are fabricated based on this design and are compared to the theoretical curves. Most devices had threshold currents between 60 and 80 mA, while laser-to-waveguide transmission coefficients were as high as 38%. >

The results of a study of the electrical and metallurgical properties of thin metallic layers deposited on InP for use as an ohmic contact are presented. A rapid thermal annealing system was used to alloy AuGe/Ni/Au contacts ton-type ion implanted InP. Rutherford backscattering and contact resistivity measurement were used to evaluate the structural and electrical characteristics of these rapid thermal alloyed thin films. Varying degrees of mixing between the metals and the semiconductor were found depending on the temperature and temperature-time cycle. These results were compared to furnace and graphite strip-heater alloying techniques. A correlation between the interface structure and the contact resistance was found. Temperatures between 430 and 450° C and alloying time of 2 sec have produced the best electrical results, with specific contact resistance as low as 2*10−7 Ω cm2 on semi-insulating InP which was Siimplanted with a peak concentration about 2*1018 cm−3. The optimum alloy temperature is marked by the onset of substantial wrinkling of the contact surface, whereas essentially smooth surfaces are obtained at temperatures below optimum. The depth of the alloyed ohmic contact is controlled by the time of heating and could be less than 1000A.

Electrical and optical properties of InP grown by low-pressure metalorganic chemical vapor deposition using triethylindium (TEI) and phosphine (PH3) are described. It was found that the net ionized impurity concentration shows a monotonic decrease as the PH3/TEI ratio increases. Similarly, the electron mobility and the photoluminescent intensity increases with the PH3/TEI ratio. The effect of growth temperature has also been investigated in the range from 500 to 650°C. For a variety of PH3/TEI ratios, the optimal growth temperature is in the range of 550×600eC. In terms of impurities, the dominant shallow acceptors are Zn and possibly C, and the most common deep acceptor is Mn. The best material obtained shows a net electron concentration of 1 × 1015 cm−3 with an associated 77K electron mobility of 41,000 cm2 /Vsec, implying that the total ionized,impurity concentration is in the range of 3'4 □ 1015 cm−3

Zinc has been selectively diffused into n-GaAs substrates with a mask of Si deposited by magnetron sputtering at room temperature. No lateral enhanced diffusion along the substrate/mask interface is observed. At the diffusion temperature of 650°C studied here, no appreciable Si diffusion into the substrate is observed.

Low-temperature photoluminescence and SEM are used to study the effects of annealing and Zn-diffusion on the doped Al0.3Ga0.7As-GaAs superlattices grown by molecular beam epitaxy. It is found that annealing has little effect on the Al-Ga interdiffusion. The photoluminescence spectra from both an unannealed and a Zn-diffused superlattice doped with Be and Sn in the wells and barriers, respectively, show peaks from the GaAs wells and the Al0.3Ga0.7As barriers. The SEM picture also shows that the superlattice remains intact with Zn-diffusion.

The first detailed report of the selective etching characteristics of an AlxGa1-xAs/GaAs DH wafer (x≥0.4) in an HF system is given. Selective etching at a cleaved facet and a calculation of the energy of activation are included.