Dislocations in Si-Doped LEC GaAs Revisited: a Spectrum Image Cathodoluminescence Study

The understanding of the role of impurities is crucial to semiconductor device technology, since all the devices are engineered by the selective incorporation of impurities. However, the incorporation of these impurities to the lattice and the resulting free charge concentration depend on the interaction with native defects. Dislocations in Si-doped substrates were studied in the nineties using highly sensitive DSL (Diluted Sirtl-Like) etching, SEM-EBIC (Electron Beam Induced Current) and microPL techniques. Both grown-in (G) dislocations, and grown-in dislocations glided (GS) by thermal stresses during post growth cooling were investigated aiming to understand the interaction between the dislocations and the doped GaAs matrix. CL spectrum imaging allows revisiting this problem supplying information about the defects forming the Cottrell atmospheres, and how they are distributed. By using a CCD multichannel detector it is possible to obtain the full spectral information over a selected area with submicrometric spatial resolution. The local spectra corresponding to the different regions of the dislocation atmosphere are available, allowing the identification of the different defects responsible for the luminescence emission. On the other hand, the use of fitting routines allows mapping the distribution of the different defects and impurities, providing a full scenario of the Cottrell atmosphere. The CL images are complemented with etching depth (using DSL) images obtained by Phase Stepping Microscopy

Developing 1D nanostructure arrays for future nanophotonics

There is intense and growing interest in one-dimensional (1-D) nanostructures from the perspective of their synthesis and unique properties, especially with respect to their excellent optical response and an ability to form heterostructures. This review discusses alternative approaches to preparation and organization of such structures, and their potential properties. In particular, molecular-scale printing is highlighted as a method for creating organized pre-cursor structure for locating nanowires, as well as vapor–liquid–solid (VLS) templated growth using nano-channel alumina (NCA), and deposition of 1-D structures with glancing angle deposition (GLAD). As regards novel optical properties, we discuss as an example, finite size photonic crystal cavity structures formed from such nanostructure arrays possessing highQand small mode volume, and being ideal for developing future nanolasers

DSL Photoetching: Principles and Application to Study Nature of Defects in III-V Materials

After a short general description of the chemical etching of semiconductors the mechanisms of defect-selective etching are described in detail. Two distinct mechanisms that lead to the formation of etch pits and etch hillocks on dislocations emerging at a semiconductor surface are discussed. The principles of the formation of defect-related etch features are described for the HF-CrO$\text{}_{3}$-H$\text{}_{2}$O etching system used for etching of GaAs. A model of surface reactions is presented and the influence of illumination during etching on the defect-selectivity is emphasized. The use of ultra sensitive photoetching to study the nature and origin of complex defects in SI and n-like GaAs is documented. In particular, the concept for the formation of dislocation cell structure in undoped GaAs is presented and the ability of photoetching to reveal the structural changes during annealing is visualized

SELECTIVE ETCHING OF n-TYPE GaAs IN A CrO3-HF-H2O SYSTEM UNDER LASER ILLUMINATION

Une grande gamme de mélanges CrO3/HF en forme diluée et sous éclairement laser (λ = 6328 Å) est utile pour révéler les défauts de GaAs {100} type n. Après une profondeur d'attaque de la surface de GaAs de 0,2-0,4 µm, les stries, dislocations, fautes d'empilement et inclusion sont révélées. Ces solutions d'attaque peuvent donc être utilisées pour étudier les défauts des couches épitaxiées de GaAs. Les traits caractéristiques des figures d'attaque sont similaires à ceux obtenus avec la méthode DABL (AB dilué sous éclairement laser) mais certaines propriétés du système CrO3-HF-H2O sont avantageuses. La composition de la solution (dans de larges limites) n'est pas critique pour la révélation des défauts (bien que la cinétique d'attaque dépende de la composition), la méthode est reproductible, il n'y a pas de précipités qui se forment dans la solution, ni d'effet mémoire. Ces solutions diluées type Sirtl sous éclairement laser (DSL) ont été calibrées avec la solution AB et composées avec la méthode DABL.A wide range of CrO3/HF mixtures in diluted form and under laser illumination (λ = 6328 Å) have been found to be useful for defect revealing in n-type {100} GaAs. After removal of 0.2 - 0.4 microns from the GaAs surface, striations, dislocations, stacking faults and inclusions are revealed, so these etchants can be used to study defects in GaAs epitaxial layers. The characteristic features of the etch figures are similar to those obtained with the DABL method (diluted AB etch under laser ill.) but some properties of the CrO3-HF-H2O system are advantageous : the composition of etchants (within wide limits) is not critical for the defect revealing mode (although the kinetics of etching are composition dependent), no precipitates are formed in solution, high reproducibility of the method, no memory effect. These diluted Sirtllike etchants used with laser (DSL) were calibrated with AB-etch and compared with the DABL method

Analysis of Large Impurity Atmospheres at Dislocations and Associated Point Defect Reactions in Differently n-Doped GaAs Crystals

The large impurity atmospheres at dislocations typical of n-type (Si- or Te-doped) CaAs crystals have been analysed by localized measurements of the free electron concentration, diffusion length and DSL etching velocity. The atmospheres always contain dopant atoms as well as point defects (complexes) whose formation and type depend on the type of dopant impurity and melt stoichiometry. The donor- or acceptor-like characteristics of such point defects (complexes) are responsible for the observed remarkable difference in the electrical and recombinative properties of the atmospheres between the differently doped crystals. The point defect reactions at the base of the formation of the slip traces are discussed. The possible mechanisms of the impurity-dislocation interaction leading to the formation of the atmospheres are also considered