Near infrared microscopy: a simple but effective technique to analyze microdefects in GaAs

In this paper we will show that IR-microscopy is a simple and effective technique to study microdefects in GaAs. Its potential has not been fully recognized in the past. Since the image contrast for IR-microscopy can be affected by several material properties, it is mandatory to perform a careful assessment whether absorption - or refraction effects are dominating. This will be discussed in detail in the first section by comparing images of identical sample areas taken with different contrast techniques: bright field, phase contrast and 'Schlieren' contrast. After proving that changes in the refractive index are dominating the image contrast, we will show that these changes are due to variations in the free charge carrier concentration, which can be imaged best by phase microscopy. In the next section four examples are presented applying phase microscopy to study inhomogeneities in doped GaAs which was grown by the Vertical Bridgman technique: annealing studies in Si-doped material, glide processes taking place during cool-down of the crystal after growth, growth striations and their thermal stability upon annealing providing information about the diffusion of Si and some observations for Te-doped material. In the third section we will discuss some applications of IR-dark field technique. This method can be employed to resolve precipitates in GaAs. Since dislocations are often decorated with As-precipitates the method also reveals the dislocation structure. Different decoration pattern and the associated dislocation structure present in VB-crystals will be discussed. Evidence will be presented that dislocation cell structures as well as dislocation lineage must be attributed to poligonisation effects after growth. The appearance of many decoration patterns indicates the importance of dislocation climb in GaAs. We will then discuss the dislocation structure of twin boundaries and finally describe the influence of stoichiometry. (orig.)SIGLEAvailable from TIB Hannover: RA 831(2939) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman