Low Voltage Scanning Electron Microscopy Cathodoluminescence Observations of Gallium Arsenide

A series of low voltage ( \u3c 5 keV) and low temperature ( \u3c 20K) cathodoluminescence (CL) measurements were performed on epitaxial gallium arsenide. The purpose of these measurements was to ascertain which factors were important in furthering the development of low voltage scanning electron microscopy (LVSEM) CL. LVSEM CL potentially offers great improvement in spatial resolution and the ability to probe the optical properties of surface states. Anomalous CL effects resulting from contamination at beam voltages below 3.5 keV have been interpreted in terms of cross-over potential phenomena. Luminescence dead layers were reduced to near zero in this regime. Excitonic processes were found to be particularly sensitive to injection level and surface conditions. Very weak free-to-bound transitions persisted down to 200 eV beam voltage

Can Photo- and Cathodoluminescence be Regarded as Complementary Techniques?

Photoluminescence (PL) usually provides macroscopic, high quality spectroscopic data. Cathodoluminescence (CL), on the other hand, offers the same information with microscopic imaging. However, replicating PL signatures in a CL system is not straightforward since matching experimental conditions, such as temperature and excitation density, is difficult. The matter is further exacerbated by inherent differences in the nature of excitation: electrons versus photons. Our work with high purity semiconductors suggests that CL is generally more sensitive to excitation circumstance than PL. For example, electrons can cause sample charging and contamination-related phenomena that dramatically affect CL. Changes in surface attributes (e.g., by chemical passivation) also affect PL and CL signals differently. Here, we extend previous work on GaAs by exploring the role of surface topography (by atomic force microscopy) and temperature (1.8K-100K) on excitonic lineshapes. We find that topographic subtleties strongly influence the character of exciton-polariton luminescence. We interpret these changes in terms of non-classical scattering phenomena derived from microscopic roughness. These microscopic changes also influence the temperature behaviour of excitons in crystals. Specifically, we find that passivated samples are brighter partly because there is a corresponding reduction in the (Arrhenius) activation energy for excitonic processes. In summary, the changes in surface topography and corresponding recombination physics seem well correlated

Spectrally Resolved Transmission Cathodoluminescence Evaluation of Vertical Cavity Surface Emitting Lasers

We describe an inexpensive addition to an existing cathodoluminescence system: Spectrally resolved transmission cathodoluminescence (SRTCL). In this technique, we couple the light emerging from beneath the sample into a vacuum compatible fiber optic cable for spectral dispersion by a conventional spectrometer. This simple approach represents a new development in the area of cathodoluminescence characterization. This exploratory study describes the preliminary results of this effort. We have applied SRTCL to the evaluation of InGaAs quantum wells, grown by molecular beam epitaxy, in vertical cavity surface emitting lasers. Results thus far support the viability of the technique. We also discuss the difficulties experienced to date and provide suggestions for future system improvements

Cathodoluminescence contrast of localized defects part I. Numerical model for simulation

Scanning Microscopy92355-366SCMI

Cathodoluminescence contrast of localized defects part II. Defect investigation

Scanning Microscopy92367-380SCMI

Investigation of dislocations in GaAs using cathodoluminescence in the scanning electron microscope

Scanning Microscopy741195-1206SCMI