Jau-Jiun Chen

Measurement of Zn0.95Cd0.05O∕ZnO (0001) heterojunction band offsets by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band (ΔEv) of Zn0.95Cd0.05O∕ZnO heterostructures grown by rf plasma-enhanced molecular-beam epitaxy. A value of ΔEv=0.17±0.03eV was obtained by using the Zn 2p energy level as a reference. Given the experimental band gap of 2.9 eV for the Zn0.95Cd0.05O, this would indicate a conduction band offset ΔEC of 0.30 eV in this system.

Effect of implant temperature on transient enhanced diffusion of boron in regrown silicon after amorphization by Si+ or Ge+ implantation

Si wafers were preamorphized by either Si+ or Ge+ ions at temperatures between 5 and 40 °C. The diffusion of low energy (4 keV) B+ implants into the preamorphized Si was studied in order to monitor the flux of interstitials from the end of range (EOR) region toward the surface. Transient enhanced diffusion (TED) in the regrown silicon was observed for all implants. Increasing the implantation temperature of the Si+ implant by as little as 15 °C can result in a marked decrease in the magnitude of the interstitial flux flowing from the EOR region toward the surface. This sensitivity to implant temperature appears to be even greater for Ge+ implants. In order to better understand this effect, detailed transmission electron microscopy (TEM) studies were conducted. As-implanted cross-sectional TEM micrographs indicate a measurable decrease in the thickness of the amorphous layer (up to 300 A) occurs when the implantation temperature increases from 5 to 40 °C as a result of ion beam induced epitaxial recrystall...

Band-edge electroluminescence from N+-implanted bulk ZnO

N+ ion implantation at moderate doses (1013–1014cm−2) into nominally undoped (n∼1017cm−3) bulk single-crystal ZnO substrates followed by annealing in the range 600–950°C was used to fabricate diodes that show visible luminescence at 300K and band-edge electroluminescence at 120K (∼390nm) under forward bias conditions. The current-voltage behavior of the diodes are characteristic of metal-insulator-semiconductor devices and suggest the implantation creates a more resistive region in the n‐ZnO in which holes are created by impact ionization during biasing, similar to the case of electroluminescence in ZnO varistors. The series resistance is only 25Ω due to the use of the conducting ZnO substrate.

Formation of p-n homojunctions in n-ZnO bulk single crystals by diffusion from a Zn3P2 source

p-n junctions have been formed in lightly n-type (1017cm−3) bulk, single-crystal ZnO substrates by diffusion of P from a Cd3P2, arsenic and red phosphorous dopant source in a closed-ampoule system. The P incorporation depth was found to be ∼200nm after diffusion at 550°C for 30min, as determined by secondary ion mass spectrometry profiling. The resulting structures show rectification, with on-off current ratios of ∼70 at +3∕−5V. The forward current ideality factor was ⩾2, consistent with multiple current transport mechanisms present in the junction, such as defect-assisted tunneling and conventional carrier recombination in the space-charge region via midgap deep levels. The forward turn-on voltage, VF was ∼4V at 300K with a specific on-state resistance (RON) of ∼21mΩcm2. The activation energy of the forward current at low forward biases was ∼1.4eV. This is also consistent with carrier recombination in the space charge region via a midgap deep level.

Comparison of Ti∕Al∕Pt∕Au and Ti∕Au Ohmic contacts on n-type ZnCdO

A comparison of Ti∕Au and Ti∕Al∕Pt∕Au Ohmic contacts on n-type Zn0.05Cd0.95O layers grown on ZnO buffer layers on GaN/sapphire templates showed a minimum contact resistivity of 2.3×10−4Ωcm2 at 500°C anneal temperature for Ti∕Al∕Pt∕Au and 1.6×10−4Ωcm2 at 450°C for Ti∕Al. The morphology of the Ti∕Al∕Pt∕Au contacts showed much better thermal stability and remained smooth until at least 450°C, whereas the Ti∕Au contacts show a reacted appearance after 350°C anneals. Auger electron spectroscopy depth profiling of the contact schemes as a function of anneal temperature suggests that the formation of TiOx phases that induce oxygen vacancies in the ZnCdO are responsible for the improved contact resistance after annealing in both types of metal schemes.

Oxide Dielectrics for Reliable Passivation of AlGaN/GaN HEMTs and Insulated Gates

Gallium Nitride (GaN) field effect transistors (FETs) have attracted considerable interest as high power electronics for use in the electric utility industry, defense and space applications, and hybrid vehicles. Research in this field has mainly focused on the III-nitride growth and processing and device design, with less effort towards the dielectric materials in these devices. The heterojunction FET structure requires a field passivation prior to packaging to reduce, or prevent formation of, surface traps that lead to current collapse, limiting the power of the device. Insulated gate FETs require a thin, stable dielectric that provides low interface traps, good conduction and valence band confinement, and high breakdown fields.