A Study of Inclusions in Indium Phosphide

Abstract

A detailed examination of unusual inclusions in InP substrates has been undertaken. Techniques employed have included optical microscopy, scanning electron microscopy, reflection and transmission x-ray topography, conventional and high voltage electron microscopy, electron diffraction, energy dispersive x-ray analysis, and Auger emission spectroscopy. Inclusions have been detected in many, but not all, undoped, Fe-, Sn-, and Ge-doped InP ingots, at densities from -I0 "~ to I04 cm-'-'. Larger inclusions consist essentially of a central core of densely tangled dislocations, surrounded by dislocation loops predominantly on {ll0} planes and extending I0-20 ~m outwards from the core. The entire complex of core plus surrounding loops results in a characteristically pitted appearance after etching, or as a region of strong contrast by x-ray topography. Smaller inclusions (-i ~m size) have been examined in electron microscope specimens foils. Some inclusions have been found at line dislocations, and it is probable that this is where the majority of inclusions originate, by a nucleation process. Attempts to determine the structure and chemical composition of the inclusions are presented and discussed.Single crystal indium phosphide is assuming increasing importance in at least three different areas of semiconductor technology. Iron-doped semi-insulating substrates with resistivities > 107 12cm are required for fabrication of indium phosphide FET's. n -T y p e substrates, usually produced by tin-doping to give carrier concentrations ,-, 1017-10 is cm -3, are required on which to grow epitaxial layers for transferred electron microwave devices. Finally, indium phosphide substrates are necessary for the growth of lattice p a r a m e t e r matched t e r n a r y (GaInAs) and quaternary (GaInAsP and GaAlInAs) epitaxial layers for various opto-electronic devices, particularly lasers, high brightness diodes, and detectors in the 1.3-1.6 ~m region.

Microdefects and electrical uniformity of InP annealed in phosphorus and iron phosphide ambiances

“…The large bright pits with specific shapes in Fig. 2a are dislocation clusters, a kind of defect in LECgrown InP [17,18]. This was revealed by the following dislocation etch study, that indicated the dislocation clusters originated from the asgrown undoped InP samples which were used for annealing.…”

“…2b shows that the surface of as-grown undoped InP wafer sample AN-01 has an 'orange peel' aspect and it is easy to discriminate between low-and high-dislocation areas. Such a surface characteristic is caused by the cell distribution of dislocations in InP [17][18][19][20]. Impurities in the sample accumulate around the dislocations by Cottrell force interaction [21,22], resulting in the 'orange peel' like surface revealed by A-B solution.…”

A Defect Etchant for <100> InGaAsP

“…Chemical etching is the simplest method for revealing dislocations and other defects in crystals. A number of papers have been published recently dealing with chemical, electrochemical, and photochemical etching of InP (7)(8)(9)(10)(11), InGaAs (12,13), and InGaAsP grown on <111> B InP (14,15). However, the <100> orientation is widely utilized for LED's, lasers, and other devices, but no chemical etchant that selectively reveals dislocations in <100> InGaAsP layers has yet been reported.…”