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

Abstract

We demonstrate that the presence of dopant atoms influences the roughness, morphology, and optical mirror properties of III-V semiconductor ͑110͒ cleavage surfaces. High concentrations of Te dopant atoms in GaAs lead to macroscopically curvatured ͑110͒ 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. ͓S0003-6951͑00͒02303-2͔Cleavage of III-V compound semiconductors in the zinc blende structure yield nearly perfect and atomically flat ͑110͒ 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 semiconductors is a very delicate process. For example, it has been demonstrated that dynamical instabilities of the fracture process can lead to rough surfaces. 2 Such low quality cleavage surfaces 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 influencing 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 GaAs 3 affects the fracture process such that very rough ͑110͒ 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 ͓110͔ 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 ͗001͘ and ͗110͘ 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 investigated on the atomic scale by scanning tunneling microscopy ͑STM͒ and macroscopically by light optical microscopy.On the macroscopic scale typical ͑110͒ cleavage surfaces of III-V semiconductors are mirror-like flat. Sometimes macroscopic cleavage steps occur, but the different macroscopic terraces of the surfaces have all the same orientation and no curvature at all. In contrast to this well known and characteristic picture, surfaces obtained by cleavage of highly Te doped GaAs (5ϫ10 18 cm Ϫ3

Toward Site-Specific Dopant Contrast in Scanning Electron Microscopy

“…Although sample cleavage provides large contrast values, there are some pitfalls. For a multilayered structure with differently doped regions the cleavage generally does not proceed along a single plane (Quadbeck et al, 2000). In our experiments we observed that each layer could be cleaved under a slightly different angle (i.e.…”

The Physics of Semiconductors

“…However, certain dopants in high concentrations, e.g. GaAs:Te, can induce a rough surface due to lattice distortion [136].…”

The Mechanistic Determination of Doping Contrast from Fermi Level Pinned Surfaces in the Scanning Electron Microscope Using Energy-Filtered Imaging and Calculated Potential Distributions

“…Such surface conditions, in the limit of vanishingly small, if not simply non-existent, patch field effects, will also practically be satisfied via FIB milling routinely employed in inline, online, atline, or offline, site-specific metrology, inspection, as well as PFA, for device and process development. Notably, as a panacea for inferior quality cleavage planes that may arise from lattice superdilation effects (Quadbeck et al, 2000), buried multilayers may be excavated using the Ga + FIB. Even so, ion implantation, redeposition, and amorphization are the byproducts constituting the surface damage that tends to pin the Fermi level towards the center of the energy band gap.…”