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We demonstrate that the presence of dopant atoms influences the roughness, morphology, and optical mirror properties of III-V semiconductor ~110! cleavage surfaces. High concentrations of Te dopant atoms in GaAs lead to macroscopically curvatured ~110! cleavage surfaces with high step concentrations. This ''glass-like'' fracture behavior is explained by the ''lattice superdilation phenomenon'' induced by high concentrations of Te dopant atoms in GaAs. © 2000 American Institute of Physics. @S0003-6951~00!02303-2# Cleavage of III-V compound semiconductors in the zinc blende structure yield nearly perfect and atomically flat ~110! surfaces. Such cleavage surfaces are well suited to be used as mirror planes of optical resonators in III-V semiconductor laser diodes.1 However, the cleavage of III-V semiconduc- tors is a very delicate process. For example, it has been dem- onstrated that dynamical instabilities of the fracture process can lead to rough surfaces.2 Such low quality cleavage sur- faces can severely limit the properties of optical resonators in semiconductor lasers and thus reduce the intensity of the laser itself. Therefore the ability to produce perfect cleavage surfaces, and naturally the understanding of the factors influ- encing the fracture process, is essential for the fabrication of high quality optical resonators. In this letter we demonstrate that the presence of dopant atoms influences the roughness and morphology of III-V semiconductor cleavage surfaces on the atomic as well as macroscopic scale. We show that the lattice superdilation phenomenon' induced by high concentrations of Te dopant atom in GaAs3 affects the fracture process such that very rough ~110! cleavage surfaces are produced. These surfaces exhibit even a ''glass-like'' fracture on the macroscopic scale making them unusable for mirrors in optical resonators. In order to determine the influence of dopant atoms on the roughness of cleavage surfaces, we investigated the cleavage properties of GaAs, GaP, and InP single crystals doped with Zn, Cd, Si, S, Sn, and Te. Each sample was well oriented along the @110# direction and we cut two cleavage slots into opposite sides along the oriented long axis. We cleaved the samples using a double wedge technique in ^001& and ^110& directions. Both cleavage directions yield similar results. All other cleavage directions were avoided, in order to exclude any possible influence of the orientation on the resulting surface morphology. The surfaces were investi- gated on the atomic scale by scanning tunneling microscopy ~STM! and macroscopically by light optical microscopy. On the macroscopic scale typical ~110! cleavage sur- faces of III-V semiconductors are mirror-like flat. Some- times macroscopic cleavage steps occur, but the different macroscopic terraces of the surfaces have all the same orien- tation and no curvature at all. In contrast to this well known and characteristic picture, surfaces obtained by cleavage of highly Te doped GaAs (531018 cm23) exhibit a pro- nounced curvature ~Fig. 1!, although exactly the same cleav- age setup and procedures were used. The light reflections on the cleavage surface shown in Fig. 1 visualize the large cur- vature of the cleavage surface of Te doped GaAs. We ob- served height differences of 0.1 mm over distances of 2 mm. Figure 1 demonstrates that the fracture is more glass-like, but not that expected for the cleavage of a material with perfect cleavage planes. Figure 2 shows STM images of the atomic-scale mor- phology of different cleavage surfaces. All surfaces investi- gated ~more than 20 samples! except those of highly Te doped GaAs ~two samples! have a relatively small density of steps and wide atomically flat terraces. This observation is independent of the material ~GaAs, InP, GaP! and of the doping ~n as well as p doping!. We could not detect any changes of the steps density for different doping concentra-

Effect of dopant atoms on the roughness of III–V semiconductor cleavage surfaces