Matthias Passlack

Ga2O3 films for electronic and optoelectronic applications

Properties of Ga2O3 thin films deposited by electron‐beam evaporation from a high‐purity single‐crystal Gd3Ga5O12 source are reported. As‐deposited Ga2O3 films are amorphous, stoichiometric, and homogeneous. Excellent uniformity in thickness and refractive index was obtained over a 2 in. wafer. The films maintain their integrity during annealing up to 800 and 1200 °C on GaAs and Si substrates, respectively. Optical properties including refractive index (n=1.84–1.88 at 980 nm wavelength) and band gap (4.4 eV) are close or identical, respectively, to Ga2O3 bulk properties. Reflectivities as low as 10−5 for Ga2O3/GaAs structures and a small absorption coefficient (≊100 cm−1 at 980 nm) were measured. Dielectric properties include a static dielectric constant between 9.9 and 10.2, which is identical to bulk Ga2O3, and electric breakdown fields up to 3.6 MV/cm. The Ga2O3/GaAs interface demonstrated a significantly higher photoluminescence intensity and thus a lower surface recombination velocity as compared to ...

QUASISTATIC AND HIGH FREQUENCY CAPACITANCE-VOLTAGE CHARACTERIZATION OF GA2O3-GAAS STRUCTURES FABRICATED BY IN SITU MOLECULAR BEAM EPITAXY

Interface properties of Ga2O3–GaAs structures fabricated using in situ multiple‐chamber molecular beam epitaxy have been investigated. The oxide films were deposited on clean, atomically ordered (100) GaAs surfaces at ≂600 °C by electron‐beam evaporation using a Gd3Ga5O12 single‐crystal source. Metal–insulator–semiconductor structures have been fabricated in order to characterize the Ga2O3–GaAs interface by capacitance–voltage measurements in quasistatic mode and at frequencies between 100 Hz and 1 MHz. The formation of inversion layers in both n and p‐type GaAs has been clearly established. Using the quasistatic/high frequency technique, the interface state density has been derived as a function of band gap energy and a midgap interface state density in the mid 1010 cm−2 eV−1 range has been inferred. Charge trapping in the oxide has been revealed as the dominant trapping mechanism.

Low D/sub it/, thermodynamically stable Ga/sub 2/O/sub 3/-GaAs interfaces: fabrication, characterization, and modeling

Thermodynamically stable, low D/sub it/ amorphous Ga/sub 2/O/sub 3/-(100) GaAs interfaces have been fabricated by extending molecular beam epitaxy (MBE) related techniques. We have investigated both in situ and ex situ Ga/sub 2/O/sub 3/ deposition schemes utilizing molecular beams of gallium oxide. The in situ technique employs Ga/sub 2/O/sub 3/ deposition on freshly grown, atomically ordered (100) GaAs epitaxial films in ultrahigh vacuum (UHV); the ex situ approach is based on thermal desorption of native GaAs oxides in UHV prior to Ga/sub 2/O/sub 3/ deposition. Unique electronic interface properties have been demonstrated for in situ fabricated Ga/sub 2/O/sub 3/-GaAs interfaces including a midgap interface state density D/sub it/ in the low 10/sup 10/ cm/sup -2/ eV/sup -1/ range and an interface recombination velocity S of 4000 cm/s. The existence of strong inversion in both n- and p-type GaAs has been clearly established. We will also discuss the excellent thermodynamic and photochemical interface stability. Ex situ fabricated Ga/sub 2/O/sub 3/-GaAs interfaces are inferior but still of a high quality with S=9000 cm/s and a corresponding D/sub it/ in the upper 10/sup 10/ cm/sup -2/ eV/sup -1/ range. We also developed a new numerical heterostructure model for the evaluation of capacitance-voltage (C-V), conductance-voltage (G-V), and photoluminescence (PL) data. The model involves selfconsistent interface analysis of electrical and optoelectronic measurement data and is tailored to the specifics of GaAs such as band-to-band luminescence and long minority carrier response time /spl tau//sub R/. We will further discuss equivalent circuits in strong inversion considering minority carrier generation using low-intensity light illumination.

Dielectric properties of electron‐beam deposited Ga2O3 films

We have fabricated high quality, dielectric Ga2O3 thin films. The films with thicknesses between 40 and 4000 A were deposited by electron‐beam evaporation using a single‐crystal high purity Gd3Ga5O12 source. Metal‐insulator‐semiconductor (MIS) and metal‐insulator‐metal structures (MIM) were fabricated in order to determine dielectric properties, which were found to depend strongly on deposition conditions such as substrate temperature and oxygen pressure. We obtained excellent dielectric properties for films deposited at substrate temperatures of 40 °C with no excess oxygen and at 125 °C with an oxygen partial pressure of 2×10−4 Torr. Specific resistivities ρ and dc breakdown fields Em of up to 6×1013 Ω cm and 2.1 MV/cm, respectively, were measured. Static dielectric constants between 9.93 and 10.2 were determined for these films. Like in other dielectrics, the current transport mechanisms are found to be bulk rather than electrode controlled.

High mobility NMOSFET structure with high-/spl kappa/ dielectric

High-/spl kappa/ NMOSFET structures designed for enhancement mode operation have been fabricated with mobilities exceeding 6000 cm/sup 2//Vs. The NMOSFET structures which have been grown by molecular beam epitaxy on 3-in semi-insulating GaAs substrate comprise a 10 nm strained InGaAs channel layer and a high-/spl kappa/ dielectric layer (/spl kappa//spl cong/20). Electron mobilities of >6000 and 3822 cm/sup 2//Vs have been measured for sheet carrier concentrations n/sub s/ of 2-3/spl times/10/sup 12/ and /spl cong/5.85/spl times/10/sup 12/ cm/sup -2/, respectively. Sheet resistivities as low as 280 /spl Omega//sq. have been obtained.

Recombination velocity at oxide–GaAs interfaces fabricated by in situ molecular beam epitaxy

The recombination velocity at oxide–GaAs interfaces fabricated by in situ multiple‐chamber molecular beam epitaxy has been investigated. Ga2O3, Al2O3, SiO2, and MgO films have been deposited on clean, atomically ordered n‐ and p‐type (100) GaAs surfaces using molecular beams of Ga–, Al–, Si–, and Mg oxide, respectively. Based on the internal quantum efficiency measured for incident light power densities 1≤P0≤104 W/cm2, the interface recombination velocity S has been inferred using a self‐consistent numerical heterostructure device model. While Al2O3–, SiO2–, and MgO–GaAs structures are characterized by an interface recombination velocity which is comparable to that of a bare GaAs surface (≂ 107 cm/s), S observed at Ga2O3–GaAs interfaces is as low as 4000–5000 cm/s. The excellent Ga2O3–GaAs interface recombination velocity is consistent with the previously reported low interface state density in the mid 1010 cm−2 eV−1 range.

Enhancement-Mode GaAs n-Channel MOSFET

This letter introduces the first enhancement-mode GaAs n-channel MOSFETs with a high channel mobility and an unpinned Fermi level at the oxide/GaAs interface. The NMOSFETs feature an In0.3Ga0.7 As channel layer, a channel mobility of up to 6207 cm2/Vmiddots, and a dielectric stack thickness of 13.1-18.7 nm. Enhancement-mode NMOSFETs with a gate length of 1 mum, a source/drain spacing of 3 mum, and a threshold voltage of 0.05 V show a saturation current, transconductance, on-resistance, and subthreshold swing of 243 mA/mm, 81 mS/mm, 8.0 Omegamiddotmm, and 162 mV/dec, respectively

1-

In this letter, 1-mum GaAs-based enhancement-mode n-channel devices with channel mobility of 5500 cm²/Vmiddots and g _m exceeding 250 mS/mm have been fabricated. The measured device parameters including threshold voltage V_th, maximum extrinsic transconductance g_m, saturation current I_dss, on-resistance R_on, and gate current are 0.11 V, 254 mS/mm, 380 mA/mm, 4.5 Omegamiddotmm, and < 56 pA for a first wafer and 0.08 V, 229 mS/mm, 443 mA/mm, 4.5 Omegamiddotmm, and < 90 pA for a second wafer, respectively. With an intrinsic transconductance g_mi of 434 mS/mm, GaAs enhancement-mode MOSFETs have reached expected intrinsic device performance

\mu\hbox{m}

Developments over the last 15 years in the areas of materials and devices have finally delivered competitive III-V MOSFETs with high mobility channels. This paper briefly reviews the above developments, discusses properties of the GdGaO/ Ga2O3 MOS systems, presents GaAs MOSFET DC and RF data, and concludes with an outlook for high indium content channel MOSFETs. GaAs based MOSFETs are potentially suitable for RF power amplification, switching, and front-end integration in mobile and wireless applications while MOSFETs with high indium content channels are of interest for future CMOS applications.

Enhancement Mode GaAs N-Channel MOSFETs With Transconductance Exceeding 250 mS/mm

Principles of operation of implant-free enhancement-mode MOSFETs (flatband MOSFET) are discussed. Epitaxial-layer structures designed for use in implant-free enhancement-mode devices and employing a high-kappa dielectric (kappacong20) and a strained InGaAs channel layer with a thickness of 10 nm have been manufactured on GaAs substrate. Proceeding from measured electron mobility mu as a function of the sheet-carrier concentration, enhancement-mode design considerations, saturation current IDss, and mobility requirements are discussed using two-dimensional device simulations. For the flatband MOSFET to compete successfully with other device designs, certain minimum channel mobilities are required. For RF applications, mu should exceed 5000 cm2/Vs while high-performance MOSFETs for digital applications may require even higher mobility for optimum operation. Finally, measured data of first 1-mum-GaAs-flatband enhancement-mode MOSFETs are presented; the saturation velocity of the InGaAs channel layer is derived; and measured IDss data are compared to the results obtained by simulations