Stefan P. Svensson

High-performance, 0.1 μm InAlAs/InGaAs high electron mobility transistors on GaAs

This letter describes the material characterization and device test of InAlAs/InGaAs high electron mobility transistors (HEMTs) grown on GaAs substrates with indium compositions and performance comparable to InP-based devices. This technology demonstrates the potential for lowered production cost of very high performance devices. The transistors were fabricated from material with room temperature channel electron mobilities and carrier concentrations of /spl mu/=10000 cm/sup 2//Vs, n=3.2/spl times/10/sup 12/ cm/sup -2/ (In=53%) and /spl mu/=11800 cm/sup 2//Vs, n=2.8/spl times/10/sup 12/ cm/sup -2/ (In=60%). A series of In=53%, 0.1/spl times/100 /spl mu/m/sup 2/ and 0.1/spl times/50 /spl mu/m/sup 2/ devices demonstrated extrinsic transconductance values greater than 1 S/mm with the best device reaching 1.074 S/mm. High-frequency testing of 0.1/spl times/50 /spl mu/m/sup 2/ discrete HEMTs up to 40 GHz and fitting of a small signal equivalent circuit yielded an intrinsic transconductance (g/sub m,i/) of 1.67 S/mm, with unity current gain frequency (f/sub T/) of 150 GHz and a maximum frequency of oscillation (f/sub max/) of 330 GHz. Transistors with In=60% exhibited an extrinsic g/sub m/ of 1.7 S/mm, which is the highest reported value for a GaAs based device.

Al–GaAs (001) Schottky barrier formation

Schottky diodes have been fabricated by in situ deposition of Al on GaAs (001) grown by molecular beam epitaxy. A detailed study of the Schottky barrier height (φb ) dependence on surface geometry and composition has been undertaken. Reconstructed, as well as very As‐ and very Ga‐rich surfaces have been prepared. For comparison also samples with a thin interfacial AlAs layer were produced. The barrier height was determined by the capacitance–voltage (C–V) and current–voltage (I–V) techniques. The quality of the material was controlled by deep level transient spectroscopy revealing a total concentration of levels in the upper part of the band gap in the mid 1012 cm−3 range. Measuring the barrier heights of different diodes across a wafer showed lateral variations which were preserved also after annealing. A number of possible explanations for these variations were investigated but none proved satisfactory. Averaging over a large number of diodes revealed no apparent reconstruction dependence of the barrier...

Photoemission studies of the band bending on MBE‐grown GaAs(001)

The band bending on GaAs(001) surfaces prepared by molecular beam epitaxy (MBE) have been studied for n‐ and p‐type materials. Surfaces with c(4×4), c(2×8), and (4×6) reconstruction ranging from As to Ga rich have been investigated. The surface symmetry was determined by reflection high energy electron diffraction (RHEED) and the position of the valence band maximum relative to the Fermi level was measured using angle resolved UV photoelectron spectroscopy (ARUPS) at normal emission. The position of the Fermi level relative to the valence band maximum was found to be ∼0.7 eV for n‐type and ∼0.5 eV for p‐type material, with a slightly increasing trend in going from Ga‐ to As‐rich surfaces. For the (4×6) reconstructed n‐type samples the growth termination method was found to have a significant influence on the band bending. The results obtained here are in very good agreement with previous measurements of the Al–GaAs(001) Schottky barrier height indicating that the electronic properties of this junction are...

Temperature and reconstruction dependence of the initial Al growth on GaAs(001)

Abstract The development of the interface between Al and MBE-grown GaAs(001) surfaces has been analyzed up to a mean Al coverage of 0.5 nm. Interdiffusion, chemical reactivity and nucleation have been studied by Auger electron spectroscopy and reflection high energy electron diffraction for the c(2 × 8) and the (4 × 6) surface reconstructions in the temperature interval 268 to 673 K. Above 550 K no nucleation was observed and the growth process was governed by As outdiffusion followed by formation of AlAs. At lower temperatures three characteristic regions of Al coverage were found. The different growth mechanisms in these regions are discussed. An AlGa exchange reaction was observed only on the Ga-rich (4 × 6) structure where it was also correlated to the nucleation. The particular deposition measurement procedure used was found to be an important parameter, since interdiffusion was observed even at room temperature. The coverage at which 3D nucleation occurred was dependent on both substrate temperature and surface reconstruction but always appeared between 1.5 and 3.5 monolayer coverage. A strong temperature dependence of the nucleation was observed.

The formation of the AuGaAs(001) interface

Abstract The formation of the AuGaAs(001) interface is studied by electron spectroscopy and electron diffraction. Sample surface and overlayers are prepared by molecular beam epitaxy. Deposition at room temperature converts the c(2 × 8) reconstruction to disorder at 1 A. The overlayer growth is laminar and crystalline gold in epitaxy with the substrate is observed at 4 A Growth. at 300°C is laminar only initially since domain growth starts at 0.5 A. At higher growth temperatures the Auger signal increases very slowly with deposition reflecting both interdiffusion and clustering. Annealing of a room-temperature grown submonolayer shows a strong substrate interaction at 300°C where also the surface content of gallium increases.

Film thickness distribution at oblique evaporation

The film thickness distribution and lateral distribution of the arrival rate of atoms or molecules at a substrate using evaporation sources with nonperpendicular and nonrotating substrates were determined for gold films and compared with two theoretical models—a cosine distribution and a Knudsen effusion model. (AIP)

Room temperature photoluminescence from modulation doped AlGaAs/InGaAs/GaAs quantum wells

The photoluminescence (PL) spectral shape and position from single, modulation doped, and undoped AlGaAs/InGaAs/GaAs quantum wells have been studied at room temperature (RT) with the purpose of evaluating the usefulness of the PL technique for verifying device material structures. Starting with a general expression for the line shape, we can qualitatively predict the spectral shape and position by evaluation of the squared overlap integrals of the four possible transitions between the two lowest states in the valence and conduction band wells. A self‐consistent calculation is used to determine the equilibrium wave functions and the energies of the bound states in the quantum well. Good agreement is found between the experimental and theoretical peak positions, and the Stark shift in the low‐energy spectral onset between doped and undoped structures also can be closely reproduced. The accuracy of the calculations has been verified by comparing structures with varying layer widths and constant In compositio...

Al–Ga–GaAs multimetal Schottky diodes prepared by MBE

Ga adsorption on a GaAs(001) c(2×8) surface prepared by MBE leads to cluster growth at room temperature. This has been observed directly from scanning electron microscopy (SEM) as well as in UV photoelectron spectra (UPS). Schottky diodes prepared from pure Ga metal show a large barrier height (φb≊1 eV). By depositing a thick Al layer on top of such a discontinous Ga film the properties of the bare areas will be characteristic for the Al–GaAs junction (φb=0.75 eV). The resulting metal semiconductor structure can be described with two parallel, ‘‘intermixed’’ diodes (Ga–GaAs and Al–GaAs) with varying relative areas depending on the amount of deposited Ga. The effective barrier height of this structure may consequently be tuned between 0.75 and 1 eV by controlling the Ga coverage on the GaAs, still retaining Al as the top metal for bonding of the device. Results are shown where the barrier has been increased from 0.75 up to 0.87 eV by a Ga surface coverage ranging from 0% to 50%.

High‐indium modulation doped field effect transistors on GaAs substrates

We have grown InxGa1−xAs modulation doped field effect transistors (MODFETs) using novel buffer layer schemes on GaAs substrates with x values up to 0.5. The MODFET active layers were grown at substrate temperatures between 500 and 520 °C and characterized by x‐ray diffraction, photoluminescence, and Hall effect measurements. MODFET devices with 0.15 μm gate length were fabricated, and dc and rf tested. Our work has indicated that the electron mobility in the MODFETs is a function of the growth mode, i.e., two‐dimensional (2D) layer‐by‐layer versus three‐dimensional island growth. MODFET performance, the ability to maintain a streaky reflection high‐energy electron diffraction pattern, as well as morphology had a very strong correlation. With these observations in mind we used a buffer layer scheme to give 2D growth fronts for InxGa1−xAs with x values up to 0.5, which is a modification of the buffer scheme described in K. Maezawa and T. Mizutani, IEEE Trans. Electron Devices 37, 1416 (1990). For In0.34Ga0...

Performance evaluation of the commercial point of inflection thermometry substrate temperature monitor

One of the first commercial point of inflection thermometry (POINTTM) systems is compared to an IRCONTM ModlinePlus Series V pyrometer, and the standard noncontact thermocouple in a Mod Gen II molecular beam epitaxy system. The standard POINTTM system was modified to include a pyrometer as an integral part of the optical system. A series of temperature measurements using these three techniques were compared on GaAs and InP substrates and during the molecular beam epitaxy growth of GaSb layers on a semi‐insulating, single‐side polished GaAs substrate. It is possible to obtain excellent agreement between the POINTTM system and pyrometer measurements over the effective operating range of the pyrometer (∼400–600 °C). We concluded that the POINTTM system performed well in its intended mode, which consists of deposition of films with band gaps larger than that of the two substrates GaAs and InP, for which the instrument is calibrated. Furthermore, for deposition of narrow band gap materials, the integration of ...