Volume 89, Issue 4, 15 February 2001
Index of content:
89(2001); http://dx.doi.org/10.1063/1.1334632View Description Hide Description
Modulation-doped two-dimensional hole gas structures consisting of a strained germanium channel on relaxed buffer layers were grown by molecular-beam epitaxy. Sample processing was optimized to substantially reduce the contribution from the parasitic conducting layers. Very high hall mobilities of 1700 cm2/V s for holes were observed at 295 K which are the highest reported to date for any kind of p-type silicon-based heterostructures. Hall measurements were carried out from 13 to 300 K to determine the temperature dependence of the mobility and carrier concentration. The carrier concentration at room temperature was and decreased by only 26% at 13 K, indicating very little parallel conduction. The high-temperature mobility obeys a behavior with which can be attributed to intraband optical phonon scattering.
Photoreflectance characterization of an AlInAs/GaInAs heterojunction bipolar transistor structure with a chirped superlattice89(2001); http://dx.doi.org/10.1063/1.1340001View Description Hide Description
We have measured the photoreflectance spectrum at 300 K from an AlInAs/GaInAs (lattice matched to InP) heterojunctionbipolar transistorstructure with a chirped superlattice (ChSl) grown by molecular-beam epitaxy. From the observed Franz–Keldysh oscillations we have evaluated the built-in dcelectric fields and associated doping levels in the n-GaInAs collector and n-AlInAs emitter regions. The oscillatory signal originating from the ChSl is caused both by the uniform quasielectric and nonuniform space-charge fields in this region.
89(2001); http://dx.doi.org/10.1063/1.1337917View Description Hide Description
Selected area electron diffraction pattern (SADP) and transmission electron microscopy(TEM)measurements were carried out to investigate the ordered structures in lattice-mismatched multiple quantum wells(MQWs). The SADP showed two sets of extra spots with asymmetrical intensity, and the high-resolution TEM image showed doublet periodicity in the contrast of the (001) lattice planes. The results of the SADP and the TEMmeasurements showed that a CuAu–I-type ordered structure was observed near the lattice-mismatched heterointerfaces. This CuAu–I-type ordered structure had an antiphase boundary in the periodically regular lattice-mismatched region. The existence of a CuAu–I-type ordered structure in MQWs might originate from the lattice mismatch between the and the layers. These results provide important information on the microstructural properties for improving operating efficiencies in long-wavelength optoelectronic devices, such as strain compensated electroabsorption modulators utilizing lattice-mismatched MQWs.