N- and p-type regions have been produced in GaN using Si+ and Mg+/P+ implantation, respectively, and subsequent annealing at ∼1100 °C. Carrier activation percentages of 93% for Si and 62% for Mg were obtained for implant doses of 5×1014 cm−2 of each element. Conversely, highly resistive regions (≳5×109 Ω/⧠) can be produced in initially n- or p- type GaN by N+ implantation and subsequent annealing at ∼750 °C. The activation energy of the deep states controlling the resistivity of these implant-isolated materials is in the range 0.8–0.9 eV. These process modules are applicable to the fabrication of a variety of different GaN-based electronic and photonic devices.
Commercially available focused ion beam (FIB) workstations with spatial resolution of 5-7 nm can prepare specimens with excellent lateral resolution. This capability has been utilized extensively by the semiconductor industry to obtain materials characterization from continually smaller areas. The FIB has been adopted generally as a preparation tool for scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ability to prepare site-specific specimens that can be removed from the bulk of a sample provides enhanced SEM and TEM analyses and new approaches for other analytical tools. Dedicated scanning transmission electron microscopy (STEM) can provide images through samples several micrometers thick. Auger electron spectroscopy (AES) can analyze with improved ability to identify a small particle. Secondary ion mass spectrometry (SIMS) can provide trace analysis at high mass resolution. Automatic operation of FIB workstations permits the creation of multiple lift-out samples without the presence of an operator.
Wet chemical etching of GaN, InN, AIN, InAIN and InGaN was investigated in various acid and base solutions at temperatures up to 75°C. Only KOH-based solutions were found to etch AIN and InAIN. No etchants were found for the other nitrides, emphasizing their extreme lack of chemical reactivity. The native oxide on most of the nitrides could be removed in potassium tetraborate at 75°C, or HC1/H2C)at 25°C.
Dry and wet etching characteristics of InN, AlN, and GaN deposited by electron cyclotron resonance metalorganic molecular beam epitaxy Electron cyclotron resonance etch rates for GaN, InN, and AlN are reported as a function of temperature for Cl 2 /H 2 /CH 4 /Ar and Cl 2 /H 2 /Ar plasmas. Using Cl 2 /H 2 /CH 4 /Ar plasma chemistry, GaN etch rates remain relatively constant from 30 to 125°C and then increase to a maximum of 2340 Å/min at 170°C. The InN etch rate decreases monotonically from 30 to 150°C and then rapidly increases to a maximum of 2300 Å/min at 170°C. This is the highest etch rate reported for this material. The AlN etch rate decreases throughout the temperature range studied with a maximum of 960 Å/min at 30°C. When CH 4 is removed from the plasma chemistry, the GaN and InN etch rates are slightly lower, with less dramatic changes with temperature. The surface composition of the III-V nitrides remains unchanged after exposure to the Cl 2 /H 2 /CH 4 /Ar plasma over the temperatures studied.
Electron cyclotron resonance plasma etch rates for GaN, InN, InAlN, AlN, and InGaN were measured for a new plasma chemistry, ICl/Ar. The effects of gas chemistry, microwave and rf power on the etch rates for these materials were examined. InN proved to be the most sensitive to the plasma composition and ion density. The GaN, InN, and InGaN etch rates reached ∼13 000, 11 500, and ∼7000 Å/min, respectively, at 250 W rf (−275 V dc) and 1000 W microwave power. The etched surface of GaN was found to be smooth, with no significant preferential loss of N from the surface at low rf powers, and no significant residue on the surface after etching.
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