| 1. |
- Bergsten, Johan, 1988, et al.
(författare)
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Low resistive Au-free, Ta-based, recessed ohmic contacts to InAlN/AlN/GaN heterostructures
- 2015
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 30:10, s. 105034-
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Tidskriftsartikel (refereegranskat)abstract
- The formation of recess etched Au-free ohmic contacts to an InAlN/AlN/GaN heterostructure is investigated. A Ta/Al/Ta metal stack is used to produce contacts with contact resistance (R-c) as low as 0.14 Omega mm. It is found that R-c decreases with increasing recess depth until the InAlN barrier is completely removed. For even deeper recesses R-c remains low but requires annealing at higher temperatures for contact formation. The lowest R-c is found for contacts where the recess etch has stopped just above the 2D electron gas channel. At this depth the contacts are also found to be less sensitive to other process parameters, such as anneal duration and temperature. An optimum bottom Ta layer thickness of 5-10 nm is found. Two reliability experiments preliminary confirm the stability of the recessed contacts.
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| 2. |
- Malmros, Anna, 1977, et al.
(författare)
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Evaluation of an InAlN/AlN/GaN HEMT with Ta-based ohmic contacts and PECVD SiN passivation
- 2014
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Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. - 1610-1642 .- 1862-6351. ; 11:3-4, s. 924-927
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Tidskriftsartikel (refereegranskat)abstract
- An InAlN/AlN/GaN HEMT with Au-free Ta-based ohmic contacts and a high-quality PECVD SiN passivation is reported. The ohmic contacts were annealed at 550 degrees C, resulting in a contact resistance of 0.64 Omm. The gate length was 50 nm. The device performance and the process were evaluated by performing DC-, pulsed IV-, RF-, and load-pull measurements. It was observed that current slump was effectively mitigated by the passivation layer. The DC channel current density increased by 71 % to 1170 mA/mm at the knee of the IV curve, and the transconductance increased from 382 to 477 mS/mm after passivation. At the same time the gate leakage increased, and the extrinsic f(max) decreased from 207 to 140 GHz. Output powers of 4.1 and 3.5 W/mm were measured after passivation at 31 and 40 GHz, respectively.
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| 3. |
- Malmros, Anna, 1977, et al.
(författare)
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Evaluation of Thermal Versus Plasma-Assisted ALD Al2O3 as Passivation for InAlN/AlN/GaN HEMTs
- 2015
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 36:3, s. 235-237
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Tidskriftsartikel (refereegranskat)abstract
- Al2O3 films deposited by thermal and plasma-assisted atomic layer deposition (ALD) were evaluated as passivation layers for InAlN/AlN/GaN HEMTs. As a reference, a comparison was made with the more conventional plasma enhanced chemical vapor deposition deposited SiNx passivation. The difference in sheet charge density, threshold voltage, f(T) and f(max) was moderate for the three samples. The gate leakage current differed by several orders of magnitude, in favor of Al2O3 passivation, regardless of the deposition method. Severe current slump was measured for the HEMT passivated by thermal ALD, whereas near-dispersion free operation was observed for the HEMT passivated by plasma-assisted ALD. This had a direct impact on the microwave output power. Large-signal measurements at 3 GHz revealed that HEMTs with Al2O3 passivation exhibited 77% higher output power using plasma-assisted ALD compared with thermal ALD.
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| 4. |
- Thanh, Thi Ngoc Do, 1984, et al.
(författare)
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Effects of Surface Passivation and Deposition Methods on the 1/f Noise Performance of AlInN/AlN/GaN High Electron Mobility Transistors
- 2015
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 36:4, s. 315-317
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Tidskriftsartikel (refereegranskat)abstract
- This letter reports on effects of Si3N4 and Al2O3 surface passivation as well as different deposition methods on the low-frequency noise (LFN) characteristics for AlInN/AlN/GaN high electron mobility transistors (HEMTs). Two samples are passivated with Al2O3, deposited by two different methods: 1) thermal atomic layer deposition (ALD) and 2) plasma-assisted ALD. The third sample is passivated with Si3N4 using plasma-enhanced chemical vapor deposition. The LFN of the three samples is measured under a bias condition relevant for amplifier and oscillator applications. It is found that the surface passivation has a major impact on the noise level. The best surface passivation, with respect to LFN, is the thermal ALD Al2O3 for which the noise current spectral density measured at 10 kHz is 1 x 10(-14) Hz(-1) for a bias of V-dd/I-dd = 10 V/80 mA. To the best of our knowledge, this result sets a standard as the best reported LFN of AlInN/GaN HEMTs. It is also in the same order as good commercial AlGaN/GaN HEMTs reported in literature and thus demonstrates that AlInN/GaN HEMTs, passivated with thermal ALD Al2O3, is a good candidate for millimeter-wave power generation.
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