J. Kwo

Surface passivation of III-V compound semiconductors using atomic-layer-deposition-grown Al2O3

Al2O3 was deposited on In0.15Ga0.85As∕GaAs using atomic-layer deposition (ALD). Without any surface preparation or postthermal treatment, excellent electrical properties of Al2O3∕InGaAs∕GaAs heterostructures were obtained, in terms of low electrical leakage current density (10−8 to 10−9A∕cm2) and low interfacial density of states (Dit) in the range of 1012cm−2eV−1. The interfacial reaction and structural properties studied by high-resolution x-ray photoelectron spectroscopy (HRXPS) and high-resolution transmission electron microscopy (HRTEM). The depth profile of HRXPS, using synchrotron radiation beam and low-energy Ar+ sputtering, exhibited no residual arsenic oxides at interface. The removal of the arsenic oxides from Al2O3∕InGaAs heterostructures during the ALD process ensures the Fermi-level unpinning, which was observed in the capacitance-voltage measurements. The HRTEM shows sharp transition from amorphous oxide to single crystalline semiconductor.

Properties of high κ gate dielectrics Gd2O3 and Y2O3 for Si

We present the materials growth and properties of both epitaxial and amorphous films of Gd2O3 (κ=14) and Y2O3 (κ=18) as the alternative gate dielectrics for Si. The rare earth oxide films were prepared by ultrahigh vacuum vapor deposition from an oxide source. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single domain films in the Mn2O3 structure. Compared to SiO2 gate oxide, the crystalline Gd2O3 and Y2O3 oxide films show a reduction of electrical leakage at 1 V by four orders of magnitude over an equivalent oxide thickness range of 10–20 A. The leakage of amorphous Y2O3 films is about six orders of magnitude better than SiO2 due to a smooth morphology and abrupt interface with Si. The absence of SiO2 segregation at the dielectric/Si interface is established from infrared absorption spectroscopy and scanning transmission electron microscopy. The amorphous Gd2O3 and Y2O3 films withstand the high temperature anneals to 850 °C and remain electrically and chemically intact.

GaAs metal-oxide-semiconductor field-effect transistor with nanometer-thin dielectric grown by atomic layer deposition

A GaAs metal–oxide–semiconductor field-effect transistor (MOSFET) with thin Al2O3 gate dielectric in nanometer (nm) range grown by atomic layer deposition is demonstrated. The nm-thin oxide layer with significant gate leakage current suppression is one of the key factors in downsizing field-effect transistors. A 1 μm gate-length depletion-mode n-channel GaAs MOSFET with an Al2O3 gate oxide thickness of 8 nm, an equivalent SiO2 thickness of ∼3 nm, shows a broad maximum transconductance of 120 mS/mm and a drain current of more than 400 mA/mm. The device shows a good linearity, low gate leakage current, and negligible hysteresis in drain current in a wide range of bias voltage.

Scanning Hall probe microscopy

We describe the implementation of a scanning Hall probe microscope of outstanding magnetic field sensitivity (∼0.1 G) and unprecedented spatial resolution (∼0.35 μm) to detect surface magnetic fields at close proximity to a sample. Our microscope combines the advantages of a submicron Hall probe fabricated on a GaAs/Al0.3Ga0.7As heterostructure chip and the scanning tunneling microscopy technique for precise positioning. We demonstrate its usefulness by imaging individual vortices in high Tc La1.85Sr0.15CuO4 films and superconducting networks, and magnetic bubble domains.

High ε gate dielectrics Gd2O3 and Y2O3 for silicon

We report on growth and characterization of both epitaxial and amorphous films Gd2O3 of (e=14) and Y2O3(e=18) as the gate dielectrics for Si prepared by ultrahigh vacuum vapor deposition. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single-domain films in the Mn2O3 structure. Typical electrical leakage results are 10−3 A/cm2 at 1 V for single domain epitaxial Gd2O3 and Y2O3 films with an equivalent SiO2 thickness, teq of 15 A, and 10−6 A/cm2 at 1 V for smooth amorphous Y2O3 films (e=18) with a teq of only 10 A. For all the Gd2O3 films, the absence of SiO2 segregation at the interface is established from infrared absorption measurements.

Evidence for weak link and anisotropy limitations on the transport critical current in bulk polycrystalline Y1Ba2Cu3Ox

Measurements of the transport critical‐current density (Jc), magnetization Jc, and magnetoresistance in a number of bulk sintered samples of Y1Ba2Cu3Ox from several different laboratories indicate that the transport Jc is limited by weak‐link regions between high Jc regions. The weak‐link Jc has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain‐boundary region in Y1Ba2Cu3Ox shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 A). The effect of intrinsic conduction anisotropy is discussed. A current‐transfer model is proposed in which weak conduction along the c axis plays a role in limiting Jc at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport Jc in bulk conductors.

GaAs MOSFET with oxide gate dielectric grown by atomic layer deposition

For the first time, a III-V compound semiconductor MOSFET with the gate dielectric grown by atomic layer deposition (ALD) is demonstrated. The novel application of the ALD process on III-V compound semiconductors affords tremendous functionality and opportunity by enabling the formation of high-quality gate oxides and passivation layers on III-V compound semiconductor devices. A 0.65-/spl mu/m gate-length depletion-mode n-channel GaAs MOSFET with an Al/sub 2/O/sub 3/ gate oxide thickness of 160 /spl Aring/ shows a gate leakage current density less than 10/sup -4/ A/cm/sup 2/ and a maximum transconductance of 130 mS/mm, with negligible drain current drift and hysteresis. A short-circuit current-gain cut-off frequency f/sub T/ of 14.0 GHz and a maximum oscillation frequency f/sub max/ of 25.2 GHz have been achieved from a 0.65-/spl mu/m gate-length device.

Zinc-indium-oxide: A high conductivity transparent conducting oxide

We report the fabrication and characterization of zinc‐indium‐oxide films with similar electrical conductivity and better transparency in both the visible and infrared compared with indium–tin–oxide, a widely used transparent conductor in many technological applications. Dramatically superior transmission properties in the 1–1.5 μm range in particular make zinc–indium–oxide attractive for use in infrared devices, where transparent electrodes are required. Resisitivities as low as 400 μΩ cm result from doping with small quantities of Sn; Al, Ga, and Ge are also effective dopants. Deposition on glass and quartz substrates as amorphous films by pulsed laser deposition and dc reactive sputtering is described.

Low interface state density oxide‐GaAs structures fabricated by in situ molecular beam epitaxy

Several oxide‐GaAs heterostructures were fabricated using in situ multiple‐chamber molecular beam epitaxy. The oxides include SiO2, MgO, and Ga2O3(Gd2O3), all evaporated by an electron beam method. The SiO2 and Ga2O3(Gd2O3) films are amorphous while the MgO films are crystalline and part of the films are epitaxially grown on GaAs(100). Among these heterostructures, the Ga2O3(Gd2O3)–GaAs shows a photoluminescence intensity comparable to that of Al0.45Ga0.55As–GaAs, and forms accumulation and inversion layers as measured from capacitance voltage measurement in quasistatic and high frequency modes.

Defect dominated charge transport in amorphous Ta2O5 thin films

Ta2O5 is a candidate for use in metal–oxide–metal (MOM) capacitors in several areas of silicon device technology. Understanding and controlling leakage current is critical for successful implementation of this material. We have studied thermal and photoconductive charge transport processes in Ta2O5 MOM capacitors fabricated by anodization, reactive sputtering, and chemical vapor deposition. We find that the results from each of these three methods are similar if one compares films that have the same thickness and electrodes. Two types of leakage current are identified: (a) a transient current that charges the bulk states of the films and (b) a steady state activated process involving electron transport via a defect band. The transient process involves either tunneling conductivity into states near the Fermi energy or ion motion. The steady state process, seen most commonly in films <300 A thick, is dominated by a large number of defects, ∼1019–1020 cm−3, located near the metal–oxide interfaces. The interi...