No abstract

Ion-depth profiling with Auger electron spectroscopy has been used to measure the interface width of MBE, VPE, and LPE At Gal _ x As-GaAs heterojunctions purposely fabricated to minimize interface width. By profiling the MBE structures with 250-eV Ar+ ions, it was possible to experimentally measure an interface width (10--90% Al p-p height) of -15 A. The measured interface width of VPE and LPE Alx Gal _ x As-GaAs was found to be -65 and 100 A, respectively. Since rectification has not in the past been observed in n-n AlxGal_xAs-GaAs heterojunctions, n-n AlxGal_xAs-GaAs heterojunctions were fabricated in this study to enhance the presence of the conductionband discontinuity (enhancing any possible rectification) by growing these heterojunctions from lightly doped (10 15 _10 16 cm -3) material; however, these heterojunctions did not exhibit rectification, in agreement with previous studies. The interface widths of these samples were then measured and found to be much smaller than present theories require to remove the barrier. Since compositional grading is not large enough to explain the absence of rectification, several alternative explanations to the absence of rectification are discussed.

A new red phosphor Ca3SiO4Cl2:Sm3+ has been synthesized and its luminescent properties have been investigated. The X-ray powder diffraction (XRD) was measured for studying the host structure. The excitation and emission spectra were measured at room temperature. The effect of Sm3+ ion content on the luminescent intensity and concentration quenching mechanism were studied. The results suggest that this phosphor maybe a good candidate of red phosphor for near UV-based white LED.

The electrical behavior of GaAs and other Schottky barriers is known to be affected by the presence of an oxide layer, but little is known of the effect of the oxide composition on the electrical characteristics (i.e., I-V and C-V). In this study, the surfaces of GaAs and AlxGa1−xAs were prepared in H2O, H2O2, and NH4OH, and electrical measurements were made of these Schottky barriers. The surface composition of these samples was studied with Auger electron spectroscopy and compared to the electrical behavior of the Schottky barriers. The presence of measurable amounts of As oxides in the oxide layer resulted in soft I-V characteristics. However, samples with predominantly Ga2O3 oxide layers (i.e., small amounts of As oxides) were found to exhibit more nearly ideal Schottky-barrier behavior, with conduction ideality values from 1.2 to 1.4.

Two intimately connected parameters are investigated: the abruptness of MBE heterojunctions and the minimum depth resolution of the sputter-Auger technique. Using 250-eV Ar+ ions and monitoring the Al LVV Auger transition, the sharpest interface measured to date (13–15 Å) is obtained. After correcting for the electron escape depth, a minimum interface width of 9 Å is obtained. Large increases in interface broadening with increasing Ar+ ion energies are observed.