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The spectral bidirectional scatter distribution function (BSDF) offers a complete description of the spectral and spatial optical characteristics of a material. Any gloss and color measurement can be related to a particular value of the BSDF, while accurate luminaire design with ray tracing software requires the BSDF of reflectors and filters. Many measuring instruments, each having particular advantages and limitations, have been reported in the literature, and an overview of these instruments is included. A measuring instrument that allows for an absolute determination of the spectral BSDF with a full three dimensional spatial coverage in both reflectance and transmittance mode, a broadband spectral coverage, a large dynamic range, a reasonable acquisition time, and a large sample illumination area is presented. The main instrument characteristics are discussed, and the measurement capabilities are illustrated.

We have studied identically prepared Au(5 nm)/n-GaAs (35 dots) and Au(65 nm)/n-GaAs (38 dots) Schottky barrier diodes (SBDs) on the same n-type GaAs single crystal. A GaAs wafer has been prepared by the usual chemical etching, and evaporation of the metal has been carried out in a conventional vacuum system. The effective Schottky barrier heights (SBHs) and ideality factors obtained from the current-voltage (I -V ) characteristics have differed from diode to diode. The SBH for the Au(5 nm)/n-GaAs diodes have ranged from 0.839 to 0.943 eV and the ideality factor n from 1.011 to 1.150. The SBH for the Au(65 nm)/n-GaAs diodes have ranged from 0.828 to 0.848 eV and the ideality factor n from 1.026 to 1.069. Our aim is to find the laterally homogeneous SBH values of the SBDs depending on Schottky metal thickness. The lateral homogeneous SBH values of 0.940 eV for the Au(5 nm)/n-GaAs and 0.866 eV for the Au(65 nm)/n-GaAs diodes have been calculated from a linear relationship between barrier height (BH) and the ideality factor, which can be explained by lateral inhomogeneities of the SBH, respectively.

A comparative study between n-GaAs/Au contacts, formed by electrochemical deposition or by vacuum evaporation, is presented. The main parameter, the barrier height B , was determined using three methods, i.e. classical current-voltage and capacitance-voltage measurements as well as STM-based ballistic electron emission microscopy (BEEM). The latter method allowed us to determine the distribution of B over the contact area on a nanometre scale and showed that the electrochemically made contacts are inhomogeneous. The main result, confirmed by the three methods, was that B was higher for the electrochemically deposited contacts than for the evaporated ones. This higher value is attributed to O − groups, present at the interface during the electrochemical metallization, and forming interfacial dipoles with the Au, leading to an increase of the barrier.

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After annealing in a H 2 atmosphere at different temperatures, 100 -oriented n-GaAs substrates were metallized with Au and Ti layers of different thicknesses to form Au/n-GaAs and Ti/n-GaAs Schottky diodes. The Schottky barrier height (SBH) variation and its dependence on subsequent N 2 annealing for these Schottky diodes have been studied by different measurement techniques (I-V, C-V and BEEM) to obtain reliable values. These methods show that pre-metallization annealing leads to a less homogeneous metal semiconductor (MS) interface. In case of thick Au layers the effective barrier height is reduced as soon as the H 2 annealing temperature reaches 300 • C. However, GaAs samples covered with thin Au layers or Ti layers do not exhibit such a barrier height reduction. The lower value in the case of thick Au layers is attributed to H + groups, present at the interface due to the annealing in H 2 atmosphere, forming interfacial dipoles with Au, leading to an inhomogeneous barrier and a decrease of the effective barrier height. It seems that these dipoles disappear again in the case of thin Au layers or are not formed with Ti. Post-metallization N 2 annealing at higher temperatures lowers the barrier height for all samples. The resulting barrier inhomogeneities are explained and analysed using the bond polarization theory of Tung ( 2001