L. Stafford

Effects of Zn content on structural and transparent conducting properties of indium-zinc oxide films grown by rf magnetron sputtering

Indium-zinc oxide (IZO) films were grown on glass substrates by rf magnetron sputtering using targets of 50mol% In2O3–50mol% In2O3(ZnO)3 and In2ZnkOk+3 (k=3, 4, 5, and 7) at room temperature and 300°C. The difference in Zn content between the films and the sputter targets varied with the growth temperature. The structural, electrical, and optical properties of the IZO films were investigated as a function of Zn content. The crystal structure of IZO films grown at room temperature changed from amorphous to crystalline at a Zn content (Zn∕(Zn+In)) of 68at.%. IZO films grown at 300°C using a target of 50% In2O3–50% In2O3(ZnO)3 had a Zn content of 40at.% and its x-ray diffraction peaks were matched with those of ITO. As the Zn content in IZO thin films grown at 300°C increased from 40to74at.%, the conductivity and optical band gap energy decreased.

Ni∕Au Ohmic contacts to p-type Mg-doped CuCrO2 epitaxial layers

Ohmic contact formation on p-type Mg-doped CuCrO2 layers grown by pulsed-laser deposition was investigated. While the current-voltage characteristics from Ti∕Au contacts showed back-to-back Schottky behavior, a specific contact resistance of ∼1×10−4Ωcm2 was achieved by using Ni instead of Ti. The contact resistivity was fairly independent of measurement temperature, suggesting that tunneling is the dominant transport mechanism. The contact resistance remained practically constant upon annealing in the 100–400°C range. Above 500°C, the morphology became rough and the contact showed rectifying behavior. This degradation resulted from both the out-diffusion of oxygen and the in-diffusion of Ni and Au in CuCrO2.

Ohmic contacts to p-type GaN based on TaN, TiN, and ZrN

Ohmic contacts to p-GaN using a Ni∕Au∕X∕Ti∕Au metallization scheme, where X is TaN, TiN, or ZrN, are reported. The dependence of the contact properties on annealing temperature (25–1000°C) in N2 is examined. For annealing temperatures greater than 500°C, the contacts display Ohmic characteristics and reach a minimum of about 2×10−4Ωcm2 after annealing at 700°C for 60s in a N2 ambient. The specific contact resistance is stable on annealing up to at least 1000°C. However, at high temperatures the morphology of the contacts are very rough and there is a large degree of intermixing between the metallic layers. The thermal stability of these contacts are superior as compared to conventional Ni∕Au, which display poor characteristics at annealing temperatures greater than 500°C.

Improved long-term thermal stability of InGaN∕GaN multiple quantum well light-emitting diodes using TiB2- and Ir-based p-Ohmic contacts

InGaN∕GaN multiple quantum well light-emitting diodes (MQW-LEDs) were fabricated with either Ni∕Au∕TiB2∕Ti∕Au or Ni∕Au∕Ir∕Au p-Ohmic contacts and annealed at 200 and 350°C for 45days. By comparison with companion devices with conventional Ni∕Au Ohmic contacts fabricated on the same wafer, MQW-LEDs with TiB2- and Ir-based Ohmic metallization schemes showed superior long-term thermal stability as judged by the change in turn-on voltage, leakage current, and output power, a promising result for applications where reliable operation at high temperature is required.

Influence of the film properties on the plasma etching dynamics of rf-sputtered indium zinc oxide layers

The etching characteristics of indium zinc oxide (IZO) films were investigated using a high-density plasma in Ar, Ar∕Cl2, and Ar∕CH4∕H2 chemistries. The IZO layers were deposited by means of rf magnetron sputtering, in which the target composition and growth temperature were varied to selectively tune the film properties. X-ray diffraction, elastic recoil detection, and Rutherford backscattering spectroscopy were used to determine the crystallization quality, atomic density, and composition of the as-deposited IZO films. As the In∕(In+Zn) composition ratio in the IZO layer increases, the etch yield in Ar and Ar∕Cl2 plasmas remains fairly constant, indicating that the etching dynamic is essentially independent of the film properties. In sharp contrast, a strong increase of the IZO etch yield with the In∕(In+Zn) fraction is observed in Ar∕CH4∕H2 plasma due to the preferential desorption of the group-III etch products. By comparing these experimental data to the predictions of a simple rate model accounting ...

Thermal stability of Ohmic contacts to InN

Ti∕Al∕Ni∕Au and Ti∕Al∕TiB2∕Ti∕Au Ohmic contacts on n-type InN were investigated as a function of annealing temperature. A minimum specific contact resistance of 1.6×10−6Ωcm−2 was obtained for the TiB2-based Ohmic contacts on n-type GaN with n∼1018cm−3 after annealing at 900°C. The minimum value with the Ni-based metallization was higher (6×10−6Ωcm2). The measurement temperature dependence of contact resistance was similar for both Ti∕Al∕TiB2∕Ti∕Au and Ti∕Al∕Ni∕Au, suggesting that the same transport mechanism was present in both types of contacts. The TiB2-based Ohmic contacts displayed superior thermal stability, suggesting that it is a superior diffusion barrier at these temperatures than Ni.

Aging and Stability of GaN High Electron Mobility Transistors and Light-Emitting Diodes With

There is interest in developing more stable contacts to a variety of GaN-based devices. In this paper, we give two examples of devices that show improved thermal stability when boride or Ir diffusion barriers are employed in ohmic-contact stacks. AlGaN/GaN high electron mobility transistors (HEMTs) were fabricated with Ti/Al/X/Ti/Au source-drain ohmic (where X is or Ir) contacts and were subjected to long-term annealing at 350 . By comparison with companion devices with conventional Ti/Al/Ni/Au ohmic contacts, the HEMTs with boride-based ohmic metal showed superior stability of both source-drain current and transconductance after 25 days of aging at 350 . The gate current for standard HEMTs increases during aging, and the standard ohmic contacts eventually fail by shorting to the gate contact. Similarly, InGaN/GaN multiple quantum well light-emitting diodes (MQW-LEDs) were fabricated with either Ni/Au//Ti/Au or Ni/Au/Ir/Au p-ohmic contacts. Both of these contacts showed superior long-term thermal stability compared to LEDs with conventional Ni/Au contacts.

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Ohmic contacts to p-type GaN were fabricated using W2B and CrB2 as diffusion barriers for a traditional Ni∕Au contact scheme. The annealing temperature dependence (25–1000°C) of contact resistance and the thermal aging characteristics at 200°C were examined. A minimum contact resistance of ∼2×10−4Ωcm2 was achieved after annealing at 700°C for 60s. These contacts also showed excellent stability as a function of aging at 200°C. Auger electron depth profiles reveal a large degree of intermixing at the GaN interface between Ni and Au.

- and Ir-Based Contacts

Ir/Au Schottky contacts and Ti/Al/Ir/Au ohmic contacts on n-type GaN were investigated as a function of annealing temperature and compared to their more common Ni-based counterparts. The Ir/Au ohmic contacts on n-type GaN with n ≈ 10 17 cm -3 exhibited barrier heights of 0.55 eV after annealing at 700°C and displayed less intermixing of the contact metals compared to Ni/Au. A minimum specific contact resistance of 1.6 X 10 -6 Ω cm -2 was obtained for the ohmic contacts on n-type GaN with n ≈ 10 18 cm -3 after annealing at 900°C. The measurement temperature dependence of contact resistance was similar for both Ti/Al/Ir/Au and Ti/Al/Ni/Au, suggesting the same transport mechanism was present in both types of contacts. The Ir-based ohmic contacts displayed superior thermal aging characteristics at 350°C. Auger electron spectroscopy showed that Ir is superior to Ni as a diffusion barrier at these moderate temperatures.

W2B and CrB2 diffusion barriers for Ni∕Au contacts to p-GaN

We report on the etching characteristics of GaAs and AlGaAs in capacitive BCl 3 /SF 6 plasmas modulated at a pulse timing of a few milliseconds. Under such conditions, we obtained GaAs etch rates in the 0.25 μm min -1 range, with selectivities over AlGaAs of ∼ 100. The effects of plasma-induced damage to GaAs were also measured by diode ideality factor and barrier height measurements. The electrical characteristics of the diodes show less prominent dry etch damage than in the continuous reactive ion-etching conditions, a promising result for optimized gate recess in the fabrication of AlGaAs/GaAs high-electron-mobility transistors.