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Topography acquisition. ZnSSe/GaAs laser structure.
Relief peculiarities of individual layers on cleavages with rough surface. The samples of heterostructures based on 3-5 or 2-6 compounds, that have zinc blend crystalline structures, are easy to cleave to form almost atomically flat cleavage surface, on which the constituting layers come out. Rather conventionally, we can imagine two possible ways of cleavage procedure of semiconductor wafer: like chopping a wood plank or like breaking a cracker. As a rule, the fist way gives the mirror-like surface; the second way leads to the stepped and rough surface. Nevertheless, the last case may be interesting, since a cleavage crack propagates perpendicular to the interfaces of the layered structure, and surface morphology of adjacent layers may change notably due to different mechanical behavior of those layers during the cleavage development.
In Fig. a) a contact AFM topography image of such prepared cleavage of ZnSSe/GaAs laser heterostructure is presented. Six regions of different surface morphology formed on the cleaved surface describe the history of the cleavage crack propagation. Indeed, relatively flat GaAs surface implies good condition for the cleavage development, whereas granular morphology of ZnSSe emitters reflects process of rather plastic rapture, than cleavage. This agrees well with more ductile behavior of ZnSe-based materials in reality, compared to the brittle GaAs. As one can see all the layers constituting the laser structure may be identified, in the agreement with the heterostructure energy band diagram (Fig. b). It is interesting to note, that, besides, a buffer GaAs region and an additional interface in N-ZnSSe emitter due to growth interruption are revealed in the image.
Fig. 1(a-c)
AFM images are obtained by commercial SPM P4 with CSC12 cantilevers.
On the next pages description of the used mode , details and grounds of image obtaining are presented.
Additional information about laser structures were received with usage of Lateral Force, Force Modulation,Contact EFM, Kelvin modes
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