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Gas-source molecular beam epitaxy (GSMBE) has been developed into a useful tool for the growth of both optical and electronic device structures. In this paper, we report on the use of tertiarybutylarsine (TBA) and tertiarybutylphosphine (TBP) in GSMBE for the growth of electronic device structures with state-of-the-art performance. Device structures based on both the In0.48Ga0.52P/GaAs and In0.53Ga 0.47As/InP lattice matched materials systems are described. The GSMBE system is based on the use of elemental Group-rn sources and employs thermal crackers for precracking TBA and TBP. Dopant sources include both elemental (Sn and Be) and vapor (CBr4 and SiBr4) sources. Device structures fabricated in the In0.48Ga0.52P/GaAs materials system include single- and double- heterojunction bipolar transistors (SHBTs and DHBTs). Device structures fabricated in the In0.53Ga0.47As/InP materials system include SHBTs, DHBTs, heterojunction field effect transistors (HFETs), and both planar and lateral resonant tunneling diodes (RTDs.) Vertically integrated HFET and multi-RTD heterostructures for high speed logic/memory are also described.
In this study, we shall first report selective-area epitaxy (SAE) of GaAs by chemical beam epitaxy (CBE) using tris-dimethylaminoarsenic (TDMAAs), a safer alternative source to arsine (AsH3), as the group V source. With triethylgallium (TEGa) and TDMAAs, true selectivity of GaAs can be achieved at a growth temperature of 470°C, which is much lower than the 600°C in the case of using TEGa and arsenic (As4) or AsH3. Secondly, we apply SAE of carbon-doped AIGaAs/GaAs to a heterojunction bipolar transistor (HBT) with a regrown external base, which exhibits a better device performance. Finally, the etching effect and the etched/regrown interface of GaAs using TDMAAs will be discussed.
We propose and demonstrate a new doping approach, i.e. intrinsic doping, for n-type modulation doping in InP-based heterostructures. Instead of the conventional method of n-type doping by shallow donor impurities, grown-in intrinsic defects are utilized to provide the required doping without external doping sources. The success of this approach is clearly demonstrated by our results from InGaAs/InP heterostructures, where the required n-type doping in the InP barriers is provided by Pin antisites, preferably introduced during off-stoichiometric growth of InP at low temperatures (LT-InP) by gas source molecular beam epitaxy. A twodimensional electron gas (2DEG) is shown to be formed near the InGaAs/InP heterointerface as a result of electron transfer from the LT-InP to the InGaAs active layer, from studies of Shubnikov-de Haas oscillations and photoluminescence. The concentration of the 2DEG is determined to be as high as 1.15×1012 cm−2, where two subbands of the 2DEG are readily occupied.
The near-infrared photoluminescence of high purity, nominally undoped MOVPE AlGaAs was investigated as a function of growth temperature, aluminum content and hydrostatic pressure. Two PL bands, observed at ˜1.1 eV and ˜0.8 eV independent of aluminum content, were attributed to oxygen-related defects based on the correlation of emission intensity and oxygen concentration. Hydrostatic pressure experiments, along with the measurement temperature dependence, suggest that the ˜0.8 eV band is due to emission from an oxygen-related mid-gap level to a shallow acceptor or the valence band, depending on temperature. A tentative defect model based on the off-center OA, defect in bulk GaAs and variations in the number of nearest neighbor aluminum atoms is proposed to explain the two PL bands and the dependence of their relative intensity on aluminum content.
AlSb and AlAsxSb1−x epitaxial films grown by metal-organic chemical vapor deposition were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. AlSb films were grown at 500°C and 76 torr using trimethylamine or ethyldimethylamine alane and triethylantimony. We examined the growth of AlAsSb using temperatures of 500 to 600 ° C, pressures of 65 to 630 torr, V/Ill ratios of 1–17, and growth rates of 0.3 to 2.7 μm/hour in a horizontal quartz reactor. SIMS showed C and 0 levels below 2 × 1018 cm−3 and 6×1018 cm−3 respectively for undoped AlSb. Similar levels of O were found in AlAs0.16Sb0.84 films but C levels were an order of magnitude less in undoped and Sn-doped AlAs0.16 Sb0.84 films. Hall measurements of AlAs0.16Sb0.84 showed hole concentrations between l×1017 cm−3 to 5×1018 cm−3 for Zn-doped material and electron concentrations in the low to mid 1018 cm−3 for Sndoped material. We have grown pseudomorphic InAs/InAsSb quantum well active regions on AlAsSb cladding layers. Photoluminescence of these layers has been observed up to 300 K.
We report on the structural characterization of InAs/(GaIn)Sb superlattices (SL) grown by solid-source molecular-beam epitaxy. SL periodicity and overall structural quality were assessed by high-resolution X-ray diffraction and Raman spectroscopy. Spectroscopic ellipsometry was found to be sensitive to the (GaIn)Sb alloy composition.
We report the results of the growth of InAsyP1−y /InP and In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 compressive strained multiple quantum wells (CSMQW) structures grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD). Our studies showed high quality 1.06 μm InAs0.21P0.79/InP CSMQW structure with 6 periods can be obtained when the growth temperature is around 650°C and the pressure in the reactor is about 20 Torr. When the well thickness and composition are tuned for wavelength around 1.30 μm, the quality of this structure degrades. By employing 1.1 μm wavelength, lattice-matched InGaAsP as the barrier layers and setting the growth temperature at 600 °C, high quality 1.30 μm wavelength In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 CSMQW materials with 10 periods can also be obtained. The materials were characterized with high resolution x-ray rocking curves, room and low temperature photoluminescence (PL). The 15K full-width-at-half-maximums (FWHM) of the PL peaks for 1.06 μm InAs0.21P0.79/InP and 1.30 μm In0.86Ga0.14AS0.51P0.49/ In0.86Ga0.14As0.33P0.67 CSMQW structures are 5.6 meV and 4.97 meV, respectively, which are among the smallest FWHMs reported up to date for these kinds of MOCVD growth materials. Buried heterostructure lasers at 1.3 μm wavelength have been obtained with the CSMQWs as the active layer.
We discuss the selective conversion of buried layers of AlGaAs to a stable oxide and the implementation of this oxide into high performance vertical-cavity surface emitting lasers (VCSELs). The rate of lateral oxidation is shown to be linear with an Arrhenius temperature dependence. The measured activation energies vary with Al composition, providing a high degree of oxidation selectivity between AIGaAs alloys. Thus buried oxide layers can be selectively fabricated within the VCSEL through small compositional variations in the AlGaAs layers. The oxidation of AlGaAs alloys, as opposed to AlAs, is found to provide robust processing of reliable lasers. The insulating and low refractive index oxide provides enhanced electrical and optical confinement for ultralow threshold currents in oxide-apertured VCSELs.
Long-wavelength (1300/1550 nm) vertical-cavity surface-emitting lasers (VCSELs) have been much more difficult to realize than VCSELs at shorter wavelengths such as 850/980 nm. The primary reason for this has been the low refractive index difference and reflectivity associated with lattice-matched InP/InGaAsP mirrors. A solution to this problem is to “wafer-fuse” high-reflectivity GaAs/AlGaAs mirrors to InP/InGaAsP active regions. This process has led to the first room-temperature continuous-wave (CW) 1.54 μm VCSELs. In this paper, we discuss two device geometries which employ wafer-fused mirrors, both of which lead to CW operation. We also discuss fabrication of WDM arrays using long-wavelength VCSELs.
We report successful application of a low-temperature-grown amorphous GaAs (a-GaAs) layer for stabilization of the fundamental transverse mode of InGaAs/GaAs vertical-cavity surface-emitting lasers. The maximum currents maintaining a stable fundamental transverse mode were increased by the antiguide effect of a-GaAs with a high refractive index. For 10-μm- and 15-μm-diameter devices, we attained a stable single-mode emission over a wide range of current. The antiguiding of transverse modes in vertical cavity buried in the high refractive cladding layer was calculated using a two-dimensional beam propagation method.
We have extended the spectrum of molecular-beam epitaxy (MBE) related techniques by introducing in-situ deposition of oxides. The oxide films have been deposited on clean, atomically ordered (100) GaAs wafer surfaces using molecular beams of gallium-, magnesium-, silicon-, or aluminum oxide. Among the fabricated oxide-GaAs heterostructures, Ga2O3-GaAs interfaces exhibit unique electronic properties including an interface state density Dit in the low 1010 cm−2eV−1 range and an interface recombination velocity S of 4000 cm/s. The formation of inversion layers in both n- and p-type GaAs has been clearly established. Further, thermodynamic and photochemical stability of excellent electronic interface properties of Ga2O3-GaAs structures has been demonstrated.
We report on the orientation dependence ((100), (110) and (111) ) of photoluminescence (PL), photoreflectance (PR) and Surface Photo-Voltage (SPV) for sulfur passivated bulk semiinsulating (SI) GaAs. Near band gap PL peak intensities (bound-exciton and acceptor-related) were enhanced following (NH4)2S or S2Cl2 treatment of GaAs for all orientations. The reduction of surface recombination velocity (from PL data) was orientation dependent and especially pronounced for the case of (111)A and (111)B orientations. The effect of thin dielectric layers deposited on S-treated surfaces was also investigated, particularly for (100) and (111)A orientations. SPV data shows a strong increase in the above band gap signal after both Streatment and dielectric film deposition, which was higher than that measured for only S-treated surfaces. PR data showed an increase in the interfacial electric field following deposition of dielectric film. The results of absolute S-surface coverage measurements using particle-induced X-ray emission measurements were correlated with the optical characteristics.
A chemical bath deposition process was used to grow thin (25–200 Å) films of cadmium sulfide on (100) InP from an aqueous solution of ammonium hydroxide, cadmium sulfate, and thiourea at 75–85 °C. Reflection high energy electron diffraction (RHEED) and transmission electron microscopy (TEM) show that ˜30 Å films are amorphous, while thicker films exhibit a cubic polycrystalline microstructure, with a preferred orientation in the  direction. X-ray photoelectron spectroscopy (XPS) shows the CdS treatment both removes the native oxides of InP and forms a stabilizing layer which protects the substrate from re-oxidation. Quasistatic capacitance-voltage response of MIS capacitors on InP, with a CdS layer between the insulator and substrate, exhibits well defined regions of accumulation, depletion, and inversion, indicating a high-quality interface region. An experimental Cmin/Cox, value of 0.28 was obtained, compared to the theoretical value of 0.07. The density of interface states (Dit) was reduced from 1012 to 1011 eV−1cm−2 after CdS treatment when calculated by the high-low method. InP MISFETs fabricated using CdS interlayers showed greatly enhanced device performance over untreated MISFETs.
In this work, power and reliability performance of pseudomorphic AIGaAs/InGaAs HEMT's are investigated by 2-D device simulation, spatially-resolved electro-luminescence, light emission spectra analysis, and gate current instabilities. A two-dimensional device simulation was used to exploit the off/on state breakdown origins in the power PHEMT's and to explore the physical mechanisms responsible for light emission in both conditions. A correlation between simulated results and light emission spectra highlights the breakdown origins in PHEMT's.
PHEMT's subjected to off-state breakdown stress and on-state hot carrier stress show changes in device characteristics. While gate leakage current, i.e. a surface leakage component associated with the surface passivation layer is reduced by these stresses, a reduction in drain current, transconductance degradation, and an increase in the impact ionization generated gate current are also observed.
Further improvement in off/on state breakdown voltages and device reliability calls for device structure optimization for lower electric field design, surface passivation treatment for lower surface leakage current, and Schottky barrier enhancement for lower gate current.
We have calculated the normalized stress σfxx/σ0 (σ0 is the stress in the large area stressor) in the stressor and σsxx/σ0 in the substrate for values of RE = Ef/Es (Ef is the Young's modulus of the stressor and Es, is the Young's modulus of the substrate) in the range 0.5 to 1.2. Substrate stresses for 13 stripe stressor samples are also calculated for RE = 0.9 which corresponds to an InGaAs stressor on GaAs with an In concentration of about 25%. It is found that for any given 1, the stress at a given depth increases monotonically as h increases (1 and h are the halfwidth and thickness of the stressor). The increase is rapid in the beginning for small value of h (l/h > 2). It becomes slow for 1/h < 2 and saturates at l/h = 0.5. For large i/h(l/h > 50) there are two stress wells in the substrate separated by a barrier. For l/h = 20 the two wells merge into one well with a flat bottom. As l/h decreases further the bottom curves downward, and for l/h < 2 the shape of the stress distribution curve resembles that of a parabola. The stress σsxx/σ0 decays rapidly with distance z from the interface. It is reduced to 1/3 of its value near the interface at z ˜ h. It is therefore necessary to construct the active layer close to the interface. Quality of the interface plays a dominant role in the Quantum structures fabricated in this manner. The shape and the strength of the stress well cannot be changed independently in these structures. We have suggested novel stressor designs to remove this limitation.
In this paper we show that unconventionally strained semiconductor heterostructures with unusual band structure exhibit novel and desirable electronic and optical properties not seen in the conventional strained materials. In addition to improving the performance of existing components, unconventional strain may be used to achieve greater functionality in novel optoelectronic devices. We give as examples three such devices that we have conceived and demonstrated, in the two areas of strain, lattice mismatch induced and thermal expansion coefficient mismatch induced. The higher performance and functionality in these devices demonstrate that strain engineered heterostructures are a very promising area for device research and development.
We have fabricated and studied injection lasers based on vertically coupled quantum dots (VECODs). VECODs are self-organized during alternate short-period GaAs-InAs (InGaAs) depositions after InAs (or InGaAs) pyramids are formed on a GaAs (100). The resulting arrangement represents laterally ordered array of nanoscale structures inserted in a GaAs matrix, where each structure is composed of several vertically merging InAs (or InGaAs) parts. VECODs are introduced in the active region of GaAs-AlGaAs double heterostructure laser. The threshold current density remarkably decreases with increase in number of periods (N) of the VECOD (down to 90 A cm-2 at 300K for N=10). The differential efficiency increases with N and the lasing occurs through ground state of quantum dot exciton up to room temperature (λ=1.05 μm).
Nanometer-sized GaAs particles embedded in SiO2 were prepared by a digital rf-sputtering method, where GaAs and SiO2 targets were alternately sputtered in an Ar atmosphere. The GaAs deposition time was kept shorter than the time required to form a continuous layer. Transmission electron microscopy (TEM) observations showed that the sizes of the GaAs particles can be controlled from 2 to 8 nm by changing the sputtering cycle time of the GaAs target. In spite of their small size, the GaAs particles have crystallinity similar to the target material without substrate heating or post annealing. It was also revealed that the mechanism of the particle growth depend on the surface migration of the precursors. The optical absorption spectra of the GaAs particles show a blue shift as large as 1.6 eV, corresponding to strong quantum confinement of electrons and holes.
Lead sulphide nanoparticles were prepared by colloidal techniques and subsequently deposited onto glass slides as uniform, dry films. In so doing, the effective bandgap of the semiconductor was increased from that of the bulk material by the quantum size effect. By varying the growth conditions, it was possible to change the mean particle size from 3nm to 7nm. This size variation was accompanied by (i) a variation in the absorption band onset of the material from 0.7μm to 1.3μm and (ii) a change in its colour from red to greyish-brown. No excitonic features were observed. TEM showed that the shape of the particles, as well as their size, was dependent on the growth conditions. Cubic and rod-like particles were grown in aqueous solution. Spherical particles preferable for optoelectronic devices were grown in methanolic/aqueous and aqueous solutions. However, these spherical particles were not as reproducible as the cubic ones.
In this paper we review and compare most of the published results on dry etching of silicon carbide using various techniques. The vast majority of reports have used RIE methods due to the wide availability of such reactors. Recently, alternative methods of magnetron enhanced RIE (MIE) and electron cyclotron resonance (ECR) plasmas have been demonstrated. MIE has resulted in extremely high etch rates and ECR etching has resulted in smooth, residue-free surfaces with an ability to control the etched profiles.