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The effects of O2 plasma treatment on both the chemical composition and work function of an indium–tin-oxide (ITO) film were investigated. ITO films were deposited on non-alkali glass substrate by super density arc plasma ion plating for application in active-matrix organic light-emitting diodes (OLEDs). The water contact angle decreased from 38 to 11° as the ITO films were treated with O2 plasma for 60 s at a plasma power of 150 W, indicating an increase in the hydrophilicity of the surface. It was found that there were no distinct changes in the microstructure or electrical properties of the ITO films with O2 plasma treatment. Synchrotron radiation photoemission spectroscopy data revealed that O2 plasma treatment decreased the amount of carbon contamination and increased the number of unscreened states of In3+ and (O2)2- peroxo species. This played the role of increasing the work function of the ITO films by 1.7 eV. As a result, the turn-on voltage of the OLED decreased markedly from 24 to 8 V and the maximum luminance value of the OLED increased to 2500 cd/m2.

Low-resistance and high-transparency cobalt-doped indium–tin oxides (ITO) showing ferromagnetic behavior were obtained by magnetron cosputtering technique. The majority of Co atoms occupied In (or Sn) sites of ITO at 8% doping, leading to hole generation and a concomitant ferromagnetic response with a maximum magnetization of approximately 0.26 µB/Co. As the Co concentration increased to 14%, oxide precipitates were formed. The resistivity at 8% doping was as low as 4.28×10-3 Ωcm. The optical transmissions at 460 nm and 520 nm reached maximums of 72.7% and 86.6%, respectively.

The interface dipole energies between tris(8-hydroxyquinoline) aluminum (Alq3) and Al/MgO (or bare Al) were in-situ measured using synchrotron radiation photoemission spectroscopy. The work function of Al/MgO is higher by 0.6 eV than that of Al. The interface dipole energies were determined to be -0.3 and 0.2 eV for Al/MgO and bare Al, respectively. Therefore, the barrier height of Al/MgO is higher by 0.3 eV than that of Al. The operating voltage at a current density of 50 mA/cm2 of inverted top-emitting organic light-emitting diode (ITOLED) using Al/MgO cathode decreased from 14.3 to 11.7 V, and the luminance value at the current density of 222 mA/cm2 of ITOLED increased from 1830 to 1950 cd/m2. Therefore, it is considered that MgO interfacial layer played a role in reducing the effective barrier height of electron injection by tunneling mechanism, leading to a reduction in turn-on voltage and luminance enhancement.

Degradation mechanism of secondary electron emission (SEE) properties in plasma-exposed MgO films was studied using three types of plasma ion; He+, Ne+, and Ar+. As the mass of impinging ions increased from He+ to Ar+, the SEE coefficient (γ) of MgO decreased from 0.0227 to 0.0175. Synchrotron radiation photoemission spectroscopy revealed that the Mg-to-O ratio significantly decreased from 1.00 to 0.79 in He plasma, to 0.73 in Ne plasma, and to 0.66 in Ar plasma. This was due to the preferential sputtering of Mg atoms by the high-mass ions, leading to the production of Mg vacancies (V centers) near the surface of MgO and the decrease in γ.

Microstructural reactions of a Pd/Ge contact to a AlGaAs/InGaAs pseudomorphic high electron mobility transistor (PHEMT) have been investigated, and the results have been used to interpret the changes of electrical properties of the PHEMT. In the as-deposited state, a ternary phase of Pd x GaAs containing excess Ge atoms is formed at the interface of Pd/GaAs. When the ohmic metals deposited were annealed at 300°C, a PdGe compound was formed and its contact resistivity was decreased to 1.2×10-7 Ω·cm2. This is due to the preferential outdiffusion of Ga atoms to the PdGe during annealing, leaving Ga vacancies behind. Simultaneously, Ge atoms are indiffused to the GaAs and occupy the Ga vacancies, converting the interfacial GaAs layer into n+-GaAs. The low-temperature PdGe ohmic contact allows changing the sequence in the formation of source/drain and gate electrodes in the PHEMT process. The device performance was remarkably improved as the annealing temperature was increased or the contact resistivity was reduced. The PHEMTs with a gate length of 1.1 µm, annealed at 300°C, exhibit maximum transconductance of 381 mS/mm.

The depth distributions of Ga vacancies in the PdGe ohmic contact on GaAs were studied by a slow positron beam technique. The results were compared with the electrical properties, to interpret the mechanisms on both the ohmic contact formation and the degradation at the PdGe/GaAs interface. The magnitude of the S parameter, reflecting the Ga vacancy concentration, at the near-interface GaAs region increases during the PdGe ohmic contact formation on GaAs. This is due to the creation of the n+-GaAs interfacial layer below the contact. The S parameter in the interfacial layer increases with the annealing temperature, which indicates the elevation of the Ga vacancy concentration. The Ga vacancies reduce the electron concentration, resulting in the degradation of the contact resistivity.

Effects of an intermediate layer, such as Mo or Ti, have been studied for developing Pd–Ge–Au based hybrid ohmic contacts in a high-low doped GaAs metal-semiconductor field-effect transistor (MESFET). The Pd–Ge–Au contact without the intermediate layer produces an alloyed AuGe contact at a high annealing temperature above 400° C. When Mo is added between Pd/Ge and Au, nonspiking Pd/Ge contact is formed at a low annealing temperature of 300° C. The addition of Ti, however, results in an ohmic contact with a low resistance of 0.43 Ω· mm in a wide annealing temperature ranging from 340 to 420° C. Auger depth profile and X-ray diffraction results suggest that the low resistance of the Pd/Ge/Ti/Au ohmic contact is due to formation both the Pd/Ge contact and AuGe contact through the appropriate control of Au indiffusion by Ti. The MESFET with the Pd/Ge/Ti/Au contact displays good DC characteristics. This supports that the Pd/Ge/Ti/Au contact is well suitable for application to high-low doped GaAs MESFETs due to its low-resistance and wide-process-window.

Penetration depth of Pd/Ge/Ti/Au ohmic contact to high-low-doped n-GaAs has been investigated using cross-sectional transmission electron microscopy, and the results are used to interpret the electrical properties. The ohmic metals do not penetrate into the GaAs substrate at 300° C, but penetrate deeper than 1000 Å into GaAs at 380° C. This is due to fast indiffusion of Au toward the GaAs substrate through the grain boundary of the PdGe compound, followed by formation of AuGa through reaction with GaAs. The deep penetration into GaAs at 380° C results in the lowest contact resistance of 0.43 Ω mm due to direct contact of ohmic metals with the buried high-doped GaAs layer.

The depth distributions of the positron annihilation in as-etched GaAs before and after the air exposure were characterized by a slow positron beams. The characteristic value of S parameter at near-surface region is decreased after the air exposure of the etched-GaAs, which indicates that the thin oxide layer is formed on the fresh surface of the etched GaAs during the air exposure. It is found that the mean diffusion length of positrons is not changed after the as-etched GaAs was exposed to air atmosphere. This implies that the trapping centers for a positron are not created below the surface by the chemisorption of oxygen atoms.

Several types of selectively doped Al x Ga1-x As/GaAs heterostructures were grown by molecular beam epitaxy, and were characterized by slow positron beams to obtain the depth distribution of vacancy-type defects. The results indicate that GaAs layers grown on Al x Ga1-x As contain a number of Ga vacancies V Ga in comparison with those grown on GaAs layers. This could be a reason for the low mobility of carriers in an inverted high-electron-mobility transistor because the V Ga in the channel layer can act as a scattering center for the motion of electrons. It is also observed that the dependence of the creation of V III, namely V Ga or V Al, in Si-doped Al x Ga1-x As on the Si concentration is much weaker than that in Si-doped GaAs.

The addition of impurities such as Be and Si during the epitaxial growth of GaAs on Si substrate by molecular beam epitaxy caused the reduction of dislocation density. This was demonstrated by the depth distribution of vacancy-type defects obtained from slow positron measurements and by etch pit observation. The slow positron beam results indicate that impurities, Si and Be, increase concentrations of Ga vacancies and interstitials in the grown GaAs, respectively. The results suggest that these defects assist the enhanced dislocation climb, resulting in the reduction of dislocation density in impurity-doped GaAs.