R. L. Hengehold

Depth‐resolved cathodoluminescence of ion‐implanted layers in zinc oxide

Single‐crystal substrates of ZnO prepared from a large boule of hydrothermally grown material were implanted with ions of Li, Na, N, P, and Ne using energies in the range 30 keV–1 MeV and doses of 1×1011–1×1016 ions/cm2 using substrates maintained at either room temperature or 475 °C. These implanted layers were studied using depth‐resolved cathodoluminescence. The spectra obtained agreed well with those expected based on a comparison of theoretical electron‐hole pair profiles and computer‐generated ion implantation profiles. The spectra of all samples implanted at 475 °C exhibited a peak near 6500 A, and a series of previously unreported phonon‐coupled peaks analogous to the well‐known CdS ’’edge’’ emission was observed to some extent in all the implanted samples, independent of implant species. The luminescence could be quenched by annealing above 600 °C and is probably a result of the formation of damage centers.

Electrical activation studies of GaN implanted with Si from low to high dose

Electrical activation studies of Si-implanted GaN grown on sapphire have been made as a function of ion dose and anneal temperature. Silicon was implanted at 200 keV with doses ranging from 1×1013 to 5×1015 cm−2 at room temperature. The samples were annealed from 1100 to 1350 °C with a 500-A-thick AlN cap in a nitrogen environment. Samples implanted with high doses (⩾1×1015 cm−2) have optimum anneal temperatures of around 1350 °C, exhibiting a nearly 100% electrical activation efficiency, whereas low dose (⩽5×1014 cm−2) samples exhibited lower activation efficiencies, but efficiencies increase with anneal temperature even after annealing at 1350 °C.

Near band‐edge photoluminescence from Si1−xGex/Si superlattices grown by molecular‐beam epitaxy

Sharp, well‐resolved near band‐edge photoluminescence (PL) has been observed from long‐period Si1−xGex/Si superlattices grown by molecular‐beam epitaxy, including PL from a 120 A Si/40 A Si1−xGex sample. The sharp PL is due to shallow bound excitons (BE), and consists of a no‐phonon (NP) line as well as phonon‐assisted lines. The exciton binding energies obtained from the temperature dependence of the BE(NP) lines are in the range of 4–6 meV.

Photoluminescence from Mg‐implanted, epitaxial, and semi‐insulating InP

Photoluminescence measurements were made to study the behavior of Mg implants in InP. Mg ions were implanted at an energy of 120 keV into vapor phase epitaxial (VPE) and Fe‐doped, semi‐insulating (SI) InP at doses of 1×1012–1×1015 cm−2 at room temperature. Encapsulation was with Si3N4 followed by face‐down annealing for 15 min at temperatures from 500 to 800 °C. Changes in excitation intensity, temperature, and dosage resulted in the identification of the Mg‐related free‐to‐acceptor and donor‐to‐acceptor transitions where the Mg ionization energy was calculated to be 39.4 meV. Annealing in the 700 and 800 °C range proved sufficient in moving impurities into substitutional sites and making the implants optically active. Activation, which is strongly dosage dependent, was optimum at an anneal temperature of 750 °C for VPE material, while for SI InP, maximum activation was achieved at 800 °C. A broad, structured emission between 1.20 and 1.38 eV was observed for anneal temperatures of 600 and 700 °C; it disa...

Optical characterization of molecular beam epitaxially grown InAsSb nearly lattice matched to GaSb

Molecular beam epitaxially (MBE)-grown InAsSb nearly lattice matched to (001) GaSb substrates has been studied by infrared absorption, photoluminescence (PL), and double crystal x-ray diffraction (DCXRD). The absorption measurements, made at temperatures of 6–295 K, resulted in determinations of the temperature and compositional dependencies of the energy gap and the absorption coefficients for InAs1−xSbx (0⩽x⩽0.192). Temperature- and laser excitation power-dependent PL measurements showed only a single band edge peak for the ternary samples (Δa/a⩽+0.623%). Both low temperature PL linewidths (as narrow as 4.3 meV) and observations of LO-phonon replicas indicate the good quality of this material. However, careful analysis of the PL data indicates that even this good material may have a tendency for phase separation resulting in compositional inhomogeneity as reported previously for MBE-grown InAsSb. (004) DCXRD measurements resulted in lattice mismatches between −0.629%⩽Δa/a⩽+0.708% for these samples, whil...

Neodymium and Erbium Implanted Gan

Strong rare earth (RE) emissions from Nd and Er implanted into MOCVD grown GaN were observed through photoluminescence (PL) with below bandgap excitation from an Ar + laser. Three well resolved manifolds of 4f lines from the crystal-field split 4 F 3/2 → 4 I 9/2 , 4 F 3/2 → 4 I 11/2 , and 4 F 3/2 → 4 I 13/2 transitions of Nd 3+ were observed at low temperature at ˜0.98, ˜1.14, and ˜1.46 μm, respectively. The Er implanted GaN showed both the 4 I 13/2 → 4 I 15/2 Er 3+ transition at ˜1.54 μm and the 4 I 11/2 → 4 I 15/2 Er 3+ transition at ˜1.00 μm. The Er luminescence at ˜1.54 μm and Nd luminescence at ˜1.1 μm persisted to room temperature. Both Er and Nd implanted samples showed increasing RE 3+ signal as annealing temperature increased from 700 to 1000 °C. The growth of new 4f crystal-field split-lines in the ˜1.54 μm 4 I 13/2 → 4 I 15/2 manifold as annealing temperature was increased to 1000 °C suggests multiple Er 3+ radiative centers.

Luminescence of thulium in III‐V semiconductors and silicon

Thulium (Tm) emissions were investigated in 390 keV, Tm‐implanted AlGaAs, GaAs, InP, and Si using photoluminescence spectroscopy. The emissions in the different semiconductors were observed in the 1.20 to 1.35‐μm region and are attributed to transitions between the crystal‐field‐split spin–orbit levels 3H5– 3H6 of Tm3+ (4f12). The main emission in GaAs is located at 1.233 μm and shows doublet structure with a width for each component of better than 0.15 meV at 6 K. Anneal temperature dependent studies identify multiple sites as the source of the Tm3+ emissions. The optimum anneal temperatures of Tm‐implanted GaAs and AlGaAs are between 725 and 750 °C, for 10‐ or 15‐min anneals, whereas InP:Tm appears to have the strongest emissions in the 575 to 625 °C temperature range. The intracenter Tm3+ emissions for Si:Tm were observed at 850 °C. Sample temperature dependent studies of Tm3+ emissions show that the sharp emissions can be seen to as high a temperature as 240 K for specific samples. Luminescence intens...

Plasmon excitation energies in ZnO, CdO, and MgO

A study has been made to experimentally determine the plasmon excitation energies in the oxides of Zn, Cd, and Mg using the reflection electron energy loss technique. The measurements were made on clean single‐crystal surfaces using electrons of 250–1000‐eV energy. Distinction was made between surface‐ and bulk‐plasmon excitation by recording the changes which occurred in the energy loss spectrum as the surface was selectively contaminated. Surface‐plasmon excitation energies of 17.0, 15.9, and 14.7 eV and bulk‐plasmon excitation energies of 18.8, 22.8, and 22.0 eV were measured for ZnO, CdO, and MgO, respectively. Comparison is made with similar data obtained from optical reflectivity and transmission electron energy loss measurements.

Er‐related deep centers in GaAs doped with Er by ion implantation and molecular beam epitaxy

Deep level transient spectroscopy (DLTS) and temperature‐dependent Hall effect measurements were performed on undoped, n‐, and p‐type GaAs doped with Er either by ion implantation or during molecular beam epitaxial (MBE) crystal growth. For light Er doping (≲1017 cm−3), a hole trap was observed at 35 meV above the valence band, whereas for heavier doping (≳5×1017 cm−3), a hole trap was observed at 360 meV. Both traps were found in both ion implanted and MBE materials. The 35 meV center is attributed to the Er atom occupying the Ga site and acting as an isovalent impurity, whereas the 360 meV center is attributed to Er in an interstitial position. Furthermore, photoluminescence and DLTS measurements of Er‐implanted GaAs revealed that both the Er3+ intra‐4f‐shell emission intensity and concentration of the deep 360 meV centers were maximized at an annealing temperature of 750 °C, and they decreased at higher temperature anneals, while the concentration of the shallow 35 meV centers increased.

Radiation-induced electron traps in Al0.14Ga0.86N by 1 MeV electron radiation

Electrical properties of defects induced in n-type molecular-beam-epitaxial-grown Al0.14Ga0.86N are studied using deep-level transient spectroscopy (DLTS) to explore the radiation tolerance of AlGaN-based electronic and optoelectronic devices. It has been found that four electron traps labeled R1(0.15±0.02eV), R2(0.21±0.02eV), R3(0.26±0.02eV), and R4(0.33±0.03eV) are created in the electron irradiated Al0.14Ga0.86N. The electron trap R4 is the most prominent radiation-induced defect in the DLTS spectrum and appears to be unique to AlGaN. Although the other radiation-induced traps anneal significantly at or below 400 K, this R4 trap is thermally stable up to 450 K, and could significantly affect the performance of AlGaN-based devices.