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The development and characterization of high-performance nanocontacts to n-GaAs are reported. The nanocontacts can be made to both undoped and p-doped low-temperature-grown GaAs ͑LTG:GaAs͒ cap layers. The geometry of the nanocontact is well characterized and requires the deposition of a 4 nm single-crystalline Au cluster onto an ohmic contact structure which features a chemically stable LTG:GaAs surface layer prepared using an ex situ chemical self-assembly technique. A self-assembled monolayer of xylyl dithiol (HS-CH 2 -C 6 H 4 -CH 2 -SH) is required to provide mechanical and electronic tethering of the Au cluster to the LTG:GaAs surface. For the case of an undoped LTG:GaAs cap layer, a specific contact resistance of 1ϫ10 Ϫ6 ⍀ cm 2 and a current density of 1ϫ10 6 A/cm 2 have been measured from scanning tunneling microscopy. When a p-doped LTG:GaAs cap layer is used, the corresponding values are 1ϫ10 Ϫ7 ⍀ cm 2 and 1 ϫ10 7 A/cm 2 , respectively. Improved surface stability as evidenced by a lower oxidation rate for p-doped LTG:GaAs provides a natural explanation for the higher-quality ohmic contact properties of the nanocontact to the p-doped LTG:GaAs cap layer.

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A lithium carbonate-based bi-layered electron injection layer was introduced into inverted organic light-emitting diodes (OLEDs) to reduce operation voltages and achieve carrier balance. Ultraviolet photoemission spectroscopy was used to confirm the existence of an interfacial dipole between the organic and lithium carbonate layers, which is a dominating factor related to the device performance. The respective maximum efficiencies of 15.9%, 16.9%, and 8.4% were achieved for blue, green, and red phosphorescent inverted OLEDs with identical architectures, indicating that carrier balance was easily obtained. Moreover, adoption of this sophisticated electron injection layer design resulted in respective turn on voltages of only 3.4 V, 3.2 V, and 3.2 V. Furthermore, the inverted OLEDs equipped with silicon dioxide nanoparticle based light-extraction films achieved an approximately 1.3 fold efficiency improvement over pristine devices due to the low refractive index of the silicon dioxide nanoparticles along with an effective scattering function. The blue, green, and red inverted OLEDs with the nanocomposite layer achieved respective peak efficiencies of 20.9%, 21.3%, and 10.1%.

The Schottky barrier behavior of a GaAs layer structure consisting of a thick n-GaAs layer, capped by a thin (3.5 nm) layer of as-grown unintentionally or Be-doped low-temperature-grown GaAs (LTG:GaAs), both grown by molecular beam epitaxy, has been studied. Nonalloyed, ex situ Schottky contacts using three different metals were fabricated on the LTG:GaAs-capped layers and on n-GaAs control samples, in order to study the interface barrier height (φb) versus the metal work function (φm). High frequency capacitance–voltage measurements, along with simulations that incorporate a complete description of the defect states in LTG:GaAs, were used to extract the φb values. The variation in φb with the metal work function is nearly six times greater in the LTG:GaAs capped contacts than in uncapped n-GaAs samples. This direct observation of Fermi level unpinning is consistent with earlier measurements that indicated the inhibited oxidation of LTG:GaAs layers in comparable structures for short air exposure times.