W. Reuter

Quantitative analysis of complex targets by proton‐induced x rays

We have explored the potential of proton‐induced x‐ray spectroscopy as a quantitative analytical technique to determine the composition of a homogeneous complex target. Direct production of x ray by protons in the low MeV range was considered using the binary encounter approximation and published data on the atomic number dependance of the stopping power. Also included is a correction scheme for secondary excitation processes if radiation is generated in the target capable of fluorescence excitation. The formalism of the correction scheme is closely related to the one commonly employed in electron microprobe spectroscopy. Our data indicate that the accuracy achievable in IIXS is of the order of ±5%, if one considers the two important corrections: (1) the difference in the stopping power properties of the composite target compared to the pure element target; (2) secondary excitation processes if required.

BAND STRUCTURE AND DIRECT TRANSITION ELECTROLUMINESCENCE IN THE In1−xGaxP ALLOYS

The position of the (1, 0, 0) minima in InP are determined from measurements in the region of interconduction band absorption. Direct transition electroluminescence in the In1−xGaxP alloys is observed over a range of alloys up to x = 0.8 and photon energies of up to 2.2 eV at 300°K and is consistent with the bandstructure determined for InP and that of GaP.

Low defect density amorphous hydrogenated silicon prepared by homogeneous chemical vapor deposition

Compositional, structural and transport data are presented for amorphous hydrogenated silicon (a‐Si:H) prepared by homogeneous chemical vapor deposition (HOMOCVD). We find a remarkable similarity in properties between HOMOCVD and plasma a‐Si:H, including a nearly identical range (250–300 °C) for the preparation of highly photoconductive films. However, unlike plasma material, HOMOCVD a‐Si:H exhibits negligible photo‐induced instabilities (Staebler–Wronski effect) and low spin concentrations over a wide span of deposition conditions. These results indicate that a significant defect‐creating reaction, most likely surface Si‐H bond scission, is occurring in the plasma environment, but absent in HOMOCVD.

Secondary ion emission from binary alloy systems. Part I: O+2 bombardment

We have studied the emission of positive atomic ions from five binary alloys: Cr‐Ni, Fe‐Ni, Cu‐Ni, Pd‐Ni, and Ag‐Pd, all under O+ 2 bombardment. Significant enhancement and suppression of ionization probabilities due to the presence of the second alloy component were observed. The alloying effect follows two general rules. The first rule states that for an alloy A‐B, where A forms a stronger oxide bond than B, the presence of A enhances the emission of B+, while the presence of B suppresses the emission of A+. The second rule states that the presence of A sharpens the energy distribution of B+, while the presence of B broadens the energy distribution of A+. X‐ray photoemission studies of the O+ 2 bombarded alloy surfaces connect the general rules with the enhanced oxidation of B and the suppressed oxidation of A in the alloys. All the cases that deviate from the rules originate from insufficient oxygen for oxidation resulting from the self‐limiting nature of oxidation by O+ 2 bombardment.

Probe layer measurements of electroluminescence excitation in ac thin‐film devices

It is found that Mn electroluminescence (EL) efficieny varies widely with the position of a Mn‐doped probe layer in a double dielectric thin‐film ZnS ac EL device. TbF3‐and Ag‐doped layers exhibit a more uniform EL efficiency. The results are consistent with impact excitation of Mn in an electric field that varies in the ZnS due to space charge. The more uniform EL efficiency probed in TbF3, in contrast, suggests that the excitation mechanisms of Tb is not primarily by hot‐electron impact in our devices.

Electron probe microanalysis

Abstract Electron probe microanalysis has been reviewed with special emphasis on beam target interactions. Methods for the quantitative interpretation of X-ray data obtained by this technique are discussed and compared. Modifications in the theory are described for the special case of the analysis of surface layers. Associated techniques, such as cathodoluminescence, Kossell diffraction and Auger electron spectroscopy are reviewed. Finally, merits and disadvantages of electron probe microanalysis are compared to other methods of surface analysis.

Secondary ion emission from binary alloy systems. Part II: Ar1 bombardment with O2 absorption

The emission of positive atomic ions from Cu‐Ni, Pd‐Ni, and Ag‐Pd alloys was studied under Ar+ bombardment with saturated O2 adsoprtion. In line with other published data on Cr‐Fe, Cr‐Ni, and Fe‐Ni alloys, these studies all agree well with two general rules porposed previously for O+2 bombardment. The first rule states that for an alloy A‐B, where A forms a stronger oxide bond than B, the presence of A enhances the emission of B+, and the presence of B suppresses the emission of A+. The second rule states that the presence of A sharpens the energy distribution of B+ while the presence of B broadens the energy distribution of A+. The experimental data fit the rules with better consistency than for the case of O+2 bombardment except in cases of low oxygen sticking coefficients on the alloy surfaces. The success of the general rules is linked with the enhanced oxidation of B and the suppressed oxidation of A in the alloy. X‐ray photoemission studies of the oxidized surfces support this explanation. Further e...

Charging effects in the secondary ion mass spectrometric analysis of targets containing low‐conductivity regions

Common ion sputtering techniques for depth profiles can cause buildup of charge in low‐conductivity regions such as p‐n junctions in semiconductors, leading to erroneous results. We analyzed Ga0.1Al0.9As liquid phase epitaxial (LPE) layers on GaAs with secondary ion mass spectrometry (SIMS) and observed that the profiles of 69Ga+ and 27Al+ in the low‐conductivity region of these Zn‐diffused LPE layers were a function of the sample bias. We noticed that this artifact was due to the shift and broadening of the secondary ion energy distributions caused by positive charging of the specimen surface. We also found that this could be effectively remedied by integrating the secondary ion yields over a wide energy range. The use of an electron flood gun reduced this charging effect, but complete charge compensation was not achieved even at electron current densities far exceeding the ion current density. This can be explained by the fact that the electron‐induced secondary electron coefficient of GaAlAs is larger ...

Preparation and Structure of Fe‐Doped EuO Films

A large increase in ferromagnetic Curie temperature from 69.5°K to ∼190°K has been observed in EuO films doped with Fe. These films retain most of the large magneto‐optic rotation of EuO (at 4.2°K) desired for beam addressable memories. However, the increase in Tc permits the operation of these devices at the more convenient liquid‐nitrogen temperature. Films were prepared by simultaneous evaporation of Eu, Eu2O3, and Fe at pressure of 2×10−5 Torr. The amount of Tc increase is strongly dependent upon composition. For example, films with the highest Tc require Fe/Fe+Eu∼0.07 and excess Eu with a typical weight ratio of Eu/Eu2O3∼1.3 as compared to ∼0.9 for pure EuO. The analysis by Seeman‐Bohlin x‐ray diffractometer shows the same NaCl structure as that of pure EuO with a slightly larger lattice parameter (5.1564 A). The doping also causes a reduction of grain size (from 200 to 120 A) and a tendency toward preferred orientation. Results of electron microprobe spectroscopy and Mossbauer measurements show that...

Anomalous diffusion behavior of Mg in GaAs

This experiment was undertaken to demonstrate that the anomalous diffusion behavior reported of Al in the alloy system (AlGa)As is not unique. The interdiffusion of Al and Ga across the buried heterojunctions between the AlAs and GaAs layers of a superlattice structure has been shown to be slow, whereas very much faster diffusion has been observed into the free surface of a GaAs wafer exposed to a saturated solution containing these two elements and Al. In this letter it is shown that Mg exhibits similar behavior and, further, a consequence is that when Mg is used to dope GaAs layers grown by liquid phase epitaxy the dopant penetrates to a significant depth in the underlying solid.