Liquid Phase Epitaxial Growth and Heterointerface Characteristics of Long-Wavelength Indium - Gallium Arsenide - Phosphide Heterostructures
Data are presented that demonstrate that the InGaAsP quaternary grown by constant temperature liquid phase epitaxy on InP substrate can, under certain growth conditions, exhibit considerably narrower diffraction profile half -widths than previously reported. The double crystal x -ray diffraction half-width is a relatively new assay of crystalline alloy compositional homogeneity, and the 13 arc sec value presented here for InGaAsP may represent a lower limit for the homogeneity of this material system, as a result of alloy effects. Bandgap and lattice constant data are given that characterize the transient composition that occurs at the onset of liquid phase epitaxial growth of InGaAsP on InP substrates. This compositional inhomogeneity, a region of significantly different bandgap and lattice constant than that of the remainder of the layer, is a result of the extreme non-equilibrium conditions that exist in the first milliseconds of growth. The data presented here indicate a shift in mismatch and bandgap of (LESSTHEQ) 16 x 10('-4) and (LESSTHEQ) 20 meV, respectively, as a result of the transient composition. These results permit a calculation of the changes in the individual solidus atomic species, which illuminate some aspects of incorporation kinetic effects. Transmission electron microscopy (TEM) data are presented that characterize the interfacial "damage" that arises during the liquid phase epitaxial growth of an arsenic -poor InGaAsP quatenary on a previously grown arsenic-rich layer. This "damage" takes the form of a ragged heterointerface with extensive dislocations and is observed for some of the heterostructures examined. Other heterostructures are demonstrated that yield high-quality interfaces in TEM, which is corroborated by their performance as room -temperature lasers. Stimulated emission data for single-well quantum well heterostructures (QWH's) permit a direct measurement of the InGaAsP-InP valence-band discontinuity ((DELTA)E(,v)). As the width of a single quantum well grows small, photogenerated electrons are poorly collected, while the heavier-mass holes are efficiently collected. Recombination between "hot" electrons and bound holes produces radiation that is depressed from the InP bandgap energy by (DELTA)E(,v), which is observed in the photoluminescence of single-well QWH's. The photoluminescence method is potentially the most direct and accurate measurement of heterojunction band discontinuities.
- Pub Date:
- Physics: Condensed Matter