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The temperature dependence of the specific contact resistance of W and WSi0.44 contacts on n+ In0.55Ga0.35N and InN was measured in the range -50 °C to 125 °C. The results were compared to theoretical values for different conduction mechanisms, to further elucidate the conduction mechanism in these contact structures. The data indicates the conduction mechanism is field emission for these contact schemes for all but as-deposited metal to InN where thermionic emission appears to be the dominant mechanism. The contacts were found to produce low specific resistance ohmic contacts to InGaN at room temperature, ϱc ∼ 10-7 Ω ·cm2 for W and ϱc of 4× 10-7 Ω ·cm for WSix. InN metallized with W produced ohmic contacts with ϱc ∼ 10-6 Ω ·cm and ϱc ∼ 10-6 Ω ·cm. for WSix at room temperature.
W, WSi0.44 and Ti/Al contacts were examined on n+ In0.65Ga0.35N, InN and In0.75Al0.25N. W was found to produce low specific contact resistance (Qc ˜ 10−7 Ω cm2) ohmic contacts to InGaN, with significant reaction between metal and semiconductor at 900 °C mainly due to out diffusion of In and N. WSix showed an as-deposited Qc of 4×10−7 Ω cm2 but this degraded significantly with subsequent annealing. Ti/Al contacts were stable to Ω 600 °C (Qc, ˜ 4×10−7 Ω cm2 at ≤600 °C). The surfaces of these contacts remain smooth to 800 °C for W and WSix and 650 °C for Ti/Al. InN contacted with W and Ti/Al produced ohmic contacts with Qc ˜ 10−7 Ω cm2 and for WSix Qc ˜ Ω cm2.All remained smooth to ˜ 600 °C, but exhibited significant interdiffusion of In, N, W and Ti respectively at higher temperatures. The contact resistances for all three metallization schemes were ≥ 10−4 Ω.cm2 on InAIN, and degrades with subsequent annealing. The Ti/Al was found to react with the InA1N above 400 °C, causing the contact resistance to increase rapidly. W and WSix proved to be more stable with Qc ˜ 10−2 and 10−3 Ω cm2 up to 650 °C and 700 °C respectively.
Quantum well microdisk laser structures have been fabricated in the GaN/InGaN, GaAs/AlGaAs and GaAs/InGaP systems using a combination of ECR dry etching (Cl2/CH4/H2/Ar, BC13/Ar or CH4/H2/Ar plasma chemistries respectively) and subsequent wet chemical etching of a buffer layer underlying the quantum wells. While wet etchants such as HF/H2O and HCI/HNO3/H2O are employed for AlGaAs and InGaP, respectively, a new KOH-based solution has been developed for AlN which is completely selective over both GaN and InGaN. Typical mask materials include PR or SiNx, while the high surface recombination velocity of exposed AlGaAs (∼105cm·sec-1) requires encapsulation with ECR-CVD SiNx to stabilize the optical properties of the modulators.
Etch rates for binary nitrides in ECR Cl2/CH4/H2/Ar are reported as a function of temperature, rf-bias, microwave power, pressure and relative gas proportions. GaN etch rates remain relatively constant from 30 to 125 °C and then increase to a maximum of 2340 Å-min−1 at 170 °C. The AIN etch rate decreases throughout the temperature range studied with a maximum of 960 Å-min−1 at 30 °C. When CH4 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 over the temperatures studied. The GaN and InN rates increase significantly with rf power, and the fastest rates for all three binaries are obtained at 2 mTorr. Surface morphology is smooth for GaN over a wide range of conditions, whereas InN surfaces are more sensitive to plasma parameters.
The III-V nitride-containing semiconductors InN, GaN, and AIN and their ternary alloys are the focus of extensive research for application to visible light emitters and as the basis for high temperature electronics. Recent advances in ion implantation doping of GaN and studies of the effect of rapid thermal annealing up to 1100 °C are making new device structures possible. Both p- and n-type implantation doping of GaN has been achieved using Mg co-implanted with P for p-type and Si-implantation for n-type. Electrical activation was achieved by rapid thermal anneals in excess of 1000 °C. Atomic force microscopy studies of the surface of GaN after a series of anneals from 750 to 1100 °C shows that the surface morphology gets smoother following anneals in Ar or N2. The photoluminescence of the annealed samples also shows enhanced bandedge emission for both annealing ambients. For the deep level emission near 2.2 eV, the sample annealed in N2 shows slightly reduced emission while the sample annealed in Ar shows increased emission. These annealing results suggest a combination of defect interactions occur during the high temperature processing.
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