Optical Characterization Methods Research Articles

Description of a scattering apparatus: application to the problems of characterization of opaque surfaces

We show how the complexity of a micropolished optical surface can be investigated in detail by measurement of the distribution of scattered light. We deal with problems of roughness anisotropy and uniformity together with cleaning problems. Experimental results concern numerous black glasses from different polishing shops and allow a determination of the polish inhomogeneity in a same glass set. After that, we present a detailed study of the apparatus function of the scatterometer, and we determine the limits of validity of our optical characterization method.

The sphere method: A new technique in linear and non-linear crystalline optical studies

We suggest a new method of optical characterization of non-linear materials which only requires knowledge of the orientation symmetry of the crystals studied. This method necessitates cutting only one crystal in this case KTiOPO 4(KTP), in sphere with a diameter of about 5 mm. The sphere is placed at the center of an Euler circle and illuminated with laser beams. Walk off angles are measured at 0.6328 μm. The directions of optical axes are determined at λ=0.6328 μm and λ=1.064 μm. We also establish the phase matching directions of KTP for the SHG of type II (1.064 μm/0.532 μm) directly.

Direct optical characterisation of DFB lasers for CPFSK system applications

We present a new optical characterisation method for single-frequency lasers that are to be applied in Gbit/s CPFSK systems. We use optical delay-demodulation to allow easy matching of the demodulator delay over a wide range of values. We show, for a particular device, that when used in a 2·4 Gbit/s CPFSK system, the modulation index must be larger than 1·0 to obtain a bit error rate below 10−11. With a modulation index of 1·5, bit error rates below 5 × 10−13 have been measured.

High-resolution optical methods for characterization of polycrystalline GaAs thin films

Two optical characterization techniques capable of high lateral spatial resolution (∼ 1 µm) are described and applied to the investigation of polycrystalline GaAs. The first technique yields the minority-carrier diffusion length and is based on a measurement of the change in photocurrent collected at a semitransparent Schottky barrier as reverse bias is varied. The second involves a measurement of photoluminescence intensity. The methods yield information about grain boundaries and granular properties, are compatible with conducting substrates, are nondestructive, and have potential for rapid data acquisition.

Optical characterization of deep O implants in GaAs

Optical methods for characterization of deep implants in semiconductors are evaluated, notably optical absorption below band-gap energies, and photoluminescence. Results from such measurements on 2–3-MeV O implants in GaAs are presented, and discussed with emphasis on possible physical interpretations of defect properties. The spectral shape of optical absorption from doses ?1014 cm−2 indicates that a description of initial damage as amorphous regions is not appropriate. It seems possible to qualitatively explain this spectral behavior before anneal as mainly due to the electronic states caused by disrupted bonds along the ion track. Photoluminescence (PL) spectra of implanted material (before as well as after anneal) can give specific information on the various defect complexes created by the treatment. Furthermore, the intensity reduction of PL due to residual recombination centers is by far the most sensitive way of detecting residual damage in the material, and thus offers several applications for evaluation of, e.g., annealing efficiency or, for low doses, annealing during implantation. Such measurements also show that there is an apparent orientation dependence on the level of damage introduced, so that 〈110〉 is most favorable, while 〈100〉 and especially 〈111〉 orientation of the GaAs surface resulted in higher damage. A characteristic annealing temperature of 460±30 °C for PL efficiency was found in n-type as well as p-type material, indicating annealing of important nonradiative recombination centers at this temperature. The ultimate result of annealing is critically dependent on the encapsulation technique, and we found that neither Al2O3 nor Si3N4 prepared by sputtering at 400 °C are satisfactory as capping material on n-GaAs, although they caused a slight reduction on the rate of Ga outdiffusion during anneal. Results from PL-profiling experiments are also discussed.

Characterization and control of threedimensional objects using fringe projection techniques

Several methods for optical comparison or characterization of threedimensional object forms are presented. By generalizing the classical techniques of production of image differences it is possible to obtain informations of differences in a threedimensional manner. The classical techniques only contain two dimensional information. The methods are based on appropriate fringe projection systems on the object.