M. H. Kim

Long‐time present tweedlike precursors and paraelectric clusters in ferroelectrics containing strong quenched randomness

Transmission electron microscopy studies of the (1−x)Pb(Mg1/3Nb2/3)O3–(x)PbTiO3 [PMN‐PT (1‐x)/x] crystalline solution have been performed for x=0.1, 0.2, 0.35, and 0.60. Bright‐field imaging has revealed a common sequence of domainlike states with increasing x. Normal micron‐sized ferroelectric domains were found for x≳0.40. Tweedlike structures were found for x∼0.35. These tweedlike structures are similar to those previously reported in premartensitic states. Paraelectric clusters were found for x<0.30. The paraelectric cluster state was characterized by the lack of self‐assembly amongst embryos and the presence of relaxor behavior in the macroscopic response characteristics. The composition PMN‐PT 65/35 was then modified with La for a detailed study of the transition between the tweedlike precursor and paraelectric cluster states with increasing impurity content.

Hydrogen passivation of C acceptors in high‐purity GaAs

The effects of hydrogenation in high‐purity p‐type GaAs grown by molecular beam epitaxy and metalorganic chemical vapor deposition have been investigated by low‐temperature photoluminescence and Hall‐effect measurements. Before hydrogenation, photoluminescence measurements showed the dominant acceptor in the original samples was C, while after hydrogenation, the concentration of electrically active C acceptors was significantly reduced and the samples were highly resistive. These electrical and spectroscopic results show that C acceptors in GaAs can be passivated by hydrogenation.

Observation of a sequence of domain-like states with increasing disorder in ferroelectrics

Abstract Transmission electron microscopy studies of the (1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT (1−x)/x) and the (Pb1−yLay)(Zr0·65Ti0·35)O3 (PLZT y/65/35) crystalline solutions have been performed...

Orientation dependent amphoteric behavior of group IV impurities in the molecular beam epitaxial and vapor phase epitaxial growth of GaAs

Abstract The incorporation and amphoteric behavior of the Group IV impurities, Si, Ge, and C, have been investigated in molecular beam epitaxial (MBE) and AsCl 3 vapor phase epitaxial (VPE) GaAs samples grown on (100), (211) and (311) substrates. Spectroscopic analysis using photothermal ionization spectroscopy and photoluminescence combined with variable temperature Hall effect measurements indicate that the amphoteric behavior of the Group IV impurities is kinetically influenced by different surface reaction processes associated with the substrate orientation. A description of the kinetic growth process has been developed which considers the bonding structure of the growth surface and the related surface reaction mechanisms of Group III, IV, and V sources in MBE and VPE growth. With these kinetically limited growth processes the experimentally observed impurity incorporation results can be explained based on the different reaction behavior associated with the surface bonding of the different adsorbed chemical species on the dynamic growth front.

Si donor neutralization in high‐purity GaAs

The effects of hydrogen plasma exposure on the concentration of donors in high‐purity lightly Si‐doped molecular beam epitaxial GaAs have been investigated by photothermal ionization spectroscopy, low‐temperature photoluminescence, capacitance‐voltage, and Hall‐effect measurements. Photothermal ionization measurements show that in addition to Si donors S and Ge donors are present in the original high‐purity samples. After hydrogenation, the Si donor concentration is significantly reduced with a corresponding increase in mobility. Low‐temperature photoluminescence also showed a decrease in the full width at half‐maximum of the neutral donor bound exciton line indicating that the total impurity concentration is reduced. These results provide spectroscopic evidence to support the neutralization of Si donors confirming earlier results of the effects of hydrogen plasma exposure in GaAs.

Influence of the substrate orientation on Si incorporation in molecular-beam epitaxial GaAs

The incorporation of Ge in GaAs layers grown simultaneously on (100), (311)A, and (311)B GaAs substrates by molecular‐beam epitaxy has been studied using Hall‐effect measurements, photothermal ionization spectroscopy, and photoluminescence. The quantitative analysis shows that Ge is more amphoteric than Si, but the orientation dependence of the amphoteric behavior of Ge is similar to Si. The amphoteric site preference of Ge is more selective for growth on the (311) polar orientation than on the (100) nonpolar orientation. Like Si, Ge incorporates predominantly as a donor in (311)B growth, while it incorporates predominantly as an acceptor in (311)A growth.

Identification of residual donors in high-purity epitaxial GaAs by magnetophotoluminescence

The magnetophotoluminescence peaks in the ‘‘two‐electron’’ satellites of the donor bound exciton transitions corresponding to the shallow donors S, Si, Ge, Sn, and Te have been identified by correlation of photoluminescence measurements with photothermal ionization measurements on the same high‐purity epitaxial GaAs samples. The magnetophotoluminescence measurements were made at 1.7 K and a magnetic field of 9.0 T. These results permit the use of magnetophotoluminescence measurements for the identification of residual donor impurity species in high‐purity GaAs.

Reduction of the acceptor impurity background in GaAs grown by molecular beam epitaxy

We report very high purity, unintentionally doped n‐type GaAs with the lowest acceptor background of all reported molecular beam epitaxy (MBE) GaAs layers. The residual acceptor concentration is 2.4×1013 cm−3 and the residual donor concentration is 1.5×1014 cm−3, yielding a compensation ratio of Na/Nd=0.160. The measured Hall mobility is 163 000 cm2/V s at 77 K with a peak value of 216 000 cm2/V s at 45.9 K. The limitations of the Hall mobility at 77 K as a figure of merit are discussed and more accurate figures of merit are considered. The initial preparation of the MBE system and the growth conditions leading to the reduced incorporation of acceptor impurities are also presented.

Residual acceptor impurities in undoped high‐purity InP grown by metalorganic chemical vapor deposition

Zn and an unidentified acceptor species, labeled A1, are the only residual acceptors that have been observed in a wide variety of undoped high‐purity InP samples grown by metalorganic chemical vapor deposition. Carbon is not incorporated at detectable concentrations as a residual acceptor in metalorganic chemical vapor deposited InP. However, the longitudinal and transverse optical phonon replicas of the free‐exciton recombination occur at the same energy as the donor/conduction band‐to‐acceptor peaks for C acceptors in low‐temperature photoluminescence spectra. Since these replicas are usually present in photoluminescence spectra measured under moderate or high optical excitation, care must be exercised so that these peaks are not misinterpreted as C‐related transitions.

GaAs with very low acceptor impurity background grown by molecular beam epitaxy

Abstract We report very high purity, MBE grown, unintentionally doped, n-type GaAs with an extremely low acceptor background. The residual acceptor concentration is 2.4×10 -3 and the residual donor concentration is 1.5×10 14 cm -3 , yielding a compensation ratio of N a / N d = 0.160. The measured Hall mobility is 163,000 cm 2 /V · at 77 K with a peak value of 216,000 cm 2 /V · at 45.9 K. The photolumminescence spectrum shows that this material is only lightly compensated and exhibits the narrow linwidths that are characteristic of high purity GaAs. Hall measurements show excellent electrical uniformity across the wafer, even at these low background doping.