Regrown Contacts Research Articles

High temperature stability of regrown and alloyed Ohmic contacts to AlGaN/GaN heterostructure up to 500 °C

This Letter reports the stability of regrown and alloyed Ohmic contacts to AlGaN/GaN-on-Si high electron mobility transistors (HEMTs) for high temperature applications up to 500 °C. Transfer length method (TLM) measurements from 25 to 500 °C in air show that the regrown contacts appear to be stable up to 500 °C during short term (approximately 1 h) testing, while alloyed contacts appear to decrease in contact resistance from 300 to 500 °C though increases in the error bounds due to increase sheet resistance make it difficult to conclude definitely. Additionally, longer term testing shows both technologies remain stable at least up to 48 h at 500 °C, after which the large increase in sheet resistance makes the measurement uncertainty too large to conclude definitively. Advanced microscopy images indicate both the regrown and alloyed contact regions remain structurally intact after prolonged high temperature exposure with no visible degradation in crystallinity or metal composition.

GaN HEMTs on Si With Regrown Contacts and Cutoff/Maximum Oscillation Frequencies of 250/204 GHz

This work demonstrates the high-frequency and high-power performance capacity of GaN high electron mobility transistors (HEMTs) on Si substrates. Using a T-gate and ${n}^{++}$ -GaN source/drain contacts, the InAlN/GaN HEMT with a gate length of 55 nm and a source-drain spacing of 175 nm shows a maximum drain current ${I}_{{D,MAX}}$ of 2.8 A/mm and a peak transconductance ${g}_{m}$ of 0.66 S/mm. The same HEMT exhibits a forward-current-gain cutoff frequency ${f}_{T}$ of 250 GHz and a maximum frequency of oscillation ${f}_{{MAX}}$ of 204 GHz. The ${I}_{{D,MAX}}$ , peak ${g}_{m}$ and ${f}_{T} -{f}_{{MAX}}$ product are among the best reported for GaN HEMTs on Si, which are very close to the state-of-the-art depletion-mode GaN HEMTs on SiC without a back barrier. Given the low cost of Si and the high compatibility with CMOS circuits, GaN HEMTs on Si prove to be particularly attractive for cost-sensitive applications.

Asymmetric InGaAs/InP MOSFETs With Source/Drain Engineering

We have developed laterally asymmetric In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/InP MOSFETs with different regrown contacts at the source (In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As) and the drain (InP). Introducing a wider bandgap material, InP, as the drain electrode, higher voltage gain g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> /g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> has been obtained with a reduced output conductance g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> and improved breakdown voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bd</sub> . For L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> = 50 nm, a high oscillation frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = 300 GHz has been obtained using an InP drain. A gate-connected field-plate has been introduced, which contributes to the device saturation with better impact ionization/band-to-band tunneling immunity.

AlGaN/GaN HEMTs on Si by MBE with regrown contacts and fT = 153 GHz

AbstractAlGaN/GaN high‐electron‐mobility transistors (HEMT) have been grown by radio frequency molecular beam epi‐taxy (RF‐MBE) on 3″ Si substrates. A record low contact resistance Rc ˜ 0.11 Ω.mm has been achieved for GaN HEMTs on Si by using non alloyed ohmic contacts regrown by MBE. Owing to the low contact resistance a 75‐nm gate length unpassivated HEMT shows intrinsic current gain cut‐off frequency fT =153 GHz, a high saturation drain current density&gt; 1.3 A/mm and a low RON of 1 Ω.mm, among the best reported for HEMTs on Si. With further scaling GaN HEMTs on Si can compete in the high‐performance RF arena with similar devices on SiC, while exploiting the many advantages of integration with Si. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Mass Transport Regrowth of GaN for Ohmic Contacts to AlGaN/GaN

A novel selective area mass transport regrowth technique for n + -GaN, requiring no Ga or Si precursor, was developed for low resistivity contact formation to AlGaN/GaN HEMTs. Masked samples were reactive ion etched followed by a short anneal in NH 3 and H 2 at 1050-1080 °C. During annealing mass transport occurred from large open areas to mask edges and narrow mask openings. Autodoping from the SiO 2 mask provided n-type doping. After depositing Ti/Al/Ni/Au contacts, the contact resistance was measured to ∼0.3 Ω mm, showing a weak dependence on the annealing temperature. Devices with regrown contacts were fabricated, achieving a power density of 4.8 W/mm at 8 GHz. The technique provides a low-cost regrowth process, with applications in particular for high Al composition AlGaN/GaN devices.

Mass Transport Regrowth of GaN for Ohmic Contacts to AlGaN/GaN

A novel selective area mass transport regrowth technique for n + -GaN, requiring no Ga or Si precursor, was developed for low resistivity contact formation to AlGaN/GaN HEMTs. Masked samples were reactive ion etched followed by a short anneal in NH 3 and H 2 at 1050-1080 °C. During annealing mass transport occurred from large open areas to mask edges and narrow mask openings. Autodoping from the SiO 2 mask provided n-type doping. After depositing Ti/Al/Ni/Au contacts, the contact resistance was measured to ∼0.3 Ω mm, showing a weak dependence on the annealing temperature. Devices with regrown contacts were fabricated, achieving a power density of 4.8 W/mm at 8 GHz. The technique provides a low-cost regrowth process, with applications in particular for high Al composition AlGaN/GaN devices.

Mass transport regrowth of GaN for ohmic contacts to AlGaN/GaN

Ohmic contacts were fabricated for AlGaN/GaN high-electron-mobility transistors by selective-area mass transport regrowth of GaN. The contact resistance ranged from 0.23 to 1.26 Ω mm for different contact areas and geometries. The average resistivity of the autodoped regrown GaN was measured to 4×10−3 Ω cm. Devices with regrown contacts were fabricated, achieving a transconductance of 210 mS/mm. The technique provides a low-cost regrowth process, with applications in particular for high Al-composition AlGaN/GaN devices.

Microwave low-noise AlGaAs/InGaAs HBT's with p/sup +/-regrown base contacts

This paper reports low-noise AlGaAs/InGaAs heterojunction bipolar transistors (HBT's) with p/sup +/-regrown base contacts. To reduce the thermal and shot noises, we have reduced R/sub B/ by using a p/sup +/-regrown base contact and have reduced /spl tau//sub B/ by using a compositionally-graded thin base layer. As a result, F/sub min/ values of 0.9, 1.1, 1.2, and 1.6 dB were obtained at 2, 6, 12, and 18 GHz, respectively. These low-noise characteristics of our HBT's show high potential for low-noise application.

Ohmic contacts to p-GaAs with p+/p regrown structures formed by metalorganic molecular beam epitaxy

Excellent ohmic contacts to p-GaAs are fabricated using selective growth by metalorganic molecular beam epitaxy. Specific contact resistance of about 5×10−8 Ω cm2 is achieved, without any heat treatment, at AuMn/Au and Ti/Pt/Au metal contacts, formed on p+-GaAs layers heavily carbon-doped to 4.4×1020 cm−3. Regrown contacts with planar and lateral p+/p structures are fabricated to clarify interface contact resistivities. A fairly low value of 7.1×10−8 Ω cm2 is established, using an equivalent circuit model, for the lateral contacts to thin p-GaAs layers, reasonably independent of its thicknesses in the range of 9.5–95 nm. These results, in addition to excellent growth selectivity, have confirmed prospects for practical use.

Frequency/temperature characteristics of Gunn devices

The variability and large magnitude of the frequency/temperature coefficient of Gunn oscillators has limited the application of these devices. The letter outlines a program of experiments and computer simulations aimed at achieving an understanding of the basic ∂f/∂T mechanism and thus producing a deep stable oscillator. Our simulations successfully predict observed trends in the ∂f/∂T behaviour of Gunn devices with both alloyed metal and n+ regrown contacts. The results of our study show that stable oscillators with a small loaded Q factor and near maximum power output are realisable.