High Electron Mobility Transistor Layer Research Articles

MOCVD Growth of High Quality InGaAs HEMT Layers on Large Scale Si Wafers for Heterogeneous Integration With Si CMOS

We report on the growth of In0.30Ga0.70As channel high electron mobility transistor (HEMT) epi-layers on a 200-mm Si substrate by metal-organic-chemical-vapor-deposition. The HEMT layers were grown on the Si substrate by using a ~3- ${\mu }\text{m}$ thick epitaxial buffer composing of a Ge layer, a GaAs layer, and a compositionally graded and strain relaxed InAlAs layer. The optimized epitaxy has a threading dislocation density of less than $2 {\times } 10^{{7}}$ cm−2 and a root mean square surface roughness of ~6.7 nm. The device active layers include a ${ {\delta } }$ -doped InAlAs bottom barrier, a ~15-nm thick InGaAs channel, a ~8-nm InGaP top barrier layer and a heavily doped InGaAs contact layer. MOSHEMTs with channel length down to 130 nm were fabricated. The devices achieve a peak transconductance of ${\sim }450 ~{\mu }\text{S}/ {\mu }\text{m}$ at ${V} _{ D}$ of 0.5 V. The peak effective mobility ( ${\mu }_{\text {eff}}$ ) in a device with a channel length of 20 $ {\mu }\text{m}$ device channel was ~3700 cm2/ $\text{V} {\cdot }\text{s}$ .

High-performance, micromachined GaN-on-Si high-electron-mobility transistor with backside diamondlike carbon/titanium heat-dissipation layer

A micromachined AlGaN/GaN high-electron-mobility transistor (HEMT) on a Si substrate with diamondlike carbon/titanium (DLC/Ti) heat-dissipation layers was investigated. Superior thermal conductivity and thermal expansion coefficient similar to that of GaN enabled DLC/Ti to efficiently dissipate the heat of the GaN power HEMT through the Si substrate via holes. This HEMT with DLC design also maintained a stable current density at bending conditions (strain: 0.01%). Infrared thermographic imaging showed that the thermal resistance of standard multi-finger power HEMT layer was 13.6 K/W and it improved to 5.3 K/W because of the micromachining process with a backside DLC/Ti composite layer. Thus, the proposed DLC/Ti heat-dissipation layer realized efficient thermal management in GaN power HEMTs.

Gate-Controlled Spin-Orbit Interaction in InAs High-Electron Mobility Transistor Layers Epitaxially Transferred onto Si Substrates

We demonstrate gate-controlled spin-orbit interaction (SOI) in InAs high-electron mobility transistor (HEMT) structures transferred epitaxially onto Si substrates. Successful epitaxial transfer of the multilayered structure after separation from an original substrate ensures that the InAs HEMT maintains a robust bonding interface and crystalline quality with a high electron mobility of 46200 cm(2)/(V s) at 77 K. Furthermore, Shubnikov-de Haas (SdH) oscillation analysis reveals that a Rashba SOI parameter (α) can be manipulated using a gate electric field for the purpose of spin field-effect transistor operation. An important finding is that the α value increases by about 30% in the InAs HEMT structure that has been transferred when compared to the as-grown structure. First-principles calculations indicate that the main causes of the large improvement in α are the bonding of the InAs HEMT active layers to a SiO2 insulating layer with a large band gap and the strain relaxation of the InAs channel layer during epitaxial transfer. The experimental results presented in this study offer a technological platform for the integration of III-V heterostructures onto Si substrates, permitting the spintronic devices to merge with standard Si circuitry and technology.

Influence of stress on structural properties of AlGaN/GaN high electron mobility transistor layers grown on 150 mm diameter Si (111) substrate

Effects of stress imposed by individual nitride layers on structural properties of an AlGaN/GaN high-electron-mobility-transistor (HEMT) structure, which was grown on a 150 mm diameter Si (111) substrate by metal-organic chemical vapor deposition employing high-temperature step-graded AlxGa1−xN/AlN buffer layers, were studied using transmission electron microscopy, visible micro-Raman spectroscopy, and high-resolution x-ray diffraction. It is revealed that all the nitride layers are more or less tensile strained on the Si (111) substrate; however, strain relaxations occurred at all the heterointerfaces except for the AlGaN/(AlN/)GaN two-dimensional electron gas interface, which is desired for achieving high performance HEMT. The wafer curvature, an important parameter for large area epitaxy of GaN-on-Si, is modeled on the basis of stress distribution within individual layers of the multilayered AlGaN/GaN HEMT structure via the close-form expression developed by Olsen and Ettenberg [J. Appl. Phys. 48, 2543 (1977)]. The evolution of wafer curvature induced by substrate thinning and stress redistribution is predicted by this model, which is further qualitatively confirmed by experimental results.

Correlation between optical and electrical properties in In0.52Al0.48As∕InxGa1−xAs metamorphic high-electron-mobility-transistor structures on GaAs substrates

4.2 K photoluminescence (PL) and 77K standard Hall-effect measurements were performed for In0.52Al0.48As∕InxGa1−xAs metamorphic high-electron-mobility-transistor (HEMT) structures grown on GaAs substrates with different indium contents in the InxGa1−xAs well or different Si delta-doping concentrations. It was found that electron concentrations increased with increasing PL intensity ratio of the “forbidden” transition (the second electron subband to the first heavy-hole subband) to the sum of the “allowed” transition (the first electron subband to the first heavy-hole subband) and the forbidden transition. And electron mobilities decreased with increasing product of the average full width at half maximum of allowed and forbidden transitions and the electron effective mass in the InxGa1−xAs quantum well. These results show that PL measurements are a good supplemental tool to Hall-effect measurements in optimization of the HEMT layer structure.

Low damage sputter deposition of tungsten for decanano compound semiconductor transistors

This article investigates sputter-induced damage caused by direct current magnetron sputter coating of tungsten on GaAs based high electron mobility transistor layer structures with channels buried less than 20nm from the surface. Van der Pauw structures were used to study the effect of tungsten sputtering on the transport properties of these shallow channels. Using this approach we established that substrate damage can be minimized by using low sputtering currents, a large source to substrate distance, and a high sputtering pressure. Unfortunately such sputtering conditions do not produce the best quality dense films necessary for device fabrication and it was necessary to establish conditions which were a compromise of film quality and substrate damage. Postsputter annealing was found to significantly reduce the damage and a loss of 10% in semiconductor conductivity was obtained for good quality tungsten films.

Material properties and performance of metamorphic optoelectronic integrated circuits grown by molecular beam epitaxy on GaAs substrates

Solid source molecular beam epitaxy was used to deposit in a continuous process an integrated metamorphic high electron mobility transistor (HEMT) and PIN photodiode structure. A metamorphic buffer layer was first grown on a GaAs substrate to expand the lattice constant to that of In0.53Ga0.47As used in the device layers. The HEMT layers were subsequently grown followed by the PIN diode structure. Cross-sectional and plan-view transmission electron micrographs showed planar layer interfaces and a dislocation density in the device layers of 1×106 cm−2. The device characteristics of the HEMT transistors were not adversely affected by growth of the PIN structure on top. Also the bandwidth and responsivity of the metamorphic PIN photodiode were comparable to an InP PIN photodiode with similar dark currents. The integrated HEMT/PIN diode circuit had a 3 dB bandwidth 20% greater than a hybrid combination of devices due to a decrease in parasitic losses from device interconnects. The frequency performances of circuits fabricated from the same wafer exhibited a high degree of uniformity.

Properties of metamorphic materials and device structures on GaAs substrates

Metamorphic layer structures grown on GaAs substrates have been characterized and fabricated into high quality electrical and optical devices. The root mean square surface roughness of the metamorphic films is <15 Å, which is smaller than most device layer thicknesses. Cross-sectional transmission electron micrographs show that the dislocations necessarily formed during growth of the metamorphic buffer layer are predominantly contained in the buffer layer. Subsequently grown device layers exhibit planar interfaces. From plan view micrographs, the dislocation density is approximately 10 6 cm −2 or less. The mobility of metamorphic high electron mobility transistor (HEMT) structures increases with indium content and is essentially equivalent to the mobility of the same structures grown lattice matched on InP substrates. The room temperature photoluminescence of transistor quantum wells is not degraded by growth on metamorphic buffer layers. High gain, low noise amplifiers have been demonstrated with long-term reliability. Metamorphic PIN photodiodes exhibit the same responsivities and bandwidths as InP PIN photodiodes. An integrated metamorphic PIN–HEMT layer structure has been grown. The responsivity of the PIN was 0.52 A/W with an unoptimized bandwidth approaching 30 GHz. The metamorphic high electron mobility transistor exhibited typical performance for current, transconductance, and pinch-off.

Study of doping concentration variation in InGaAs/InP high electron mobility transistor layer structures by Raman scattering

The effect of varying the dopant concentration (ND) in the InP donor layer of In0.53Ga0.47As/InP high-electron mobility transistor (HEMT) structure was studied by Raman scattering measurements. The carrier concentration in the InGaAs channel was found to increase when the doping concentration in the donor layer was increased assuming that the donors are fully ionized. The coupled mode between the InGaAs longitudinal optical phonons and the electrons in the InGaAs channel shifts continuously to a lower wave number with the increase in the value of ND in the InP donor layer. The correlation between the observed Raman shift with the carrier concentration in the channel layer can be used to characterize the HEMT structures nondestructively.

An InAlAs-InGaAs OPFET with responsivity above 200 A/W at 1.3-μm wavelength

The optoelectronic dc and RF behaviour of an InAlAs-InGaAs optically controlled field-effect transistor based on a high electron mobility transistor layer structure is investigated at 1.3-μm wavelength light. The device is backside-illuminated to increase the responsivity. A transistor with 0.3-μm gate length and an active area of 50×50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> exhibits a responsivity of 235 A/W, at 11-μW incident optical power. The photoconductive response is higher than for an metal-semiconductor-metal photodetector with the same InGaAs absorption layer thickness up to 10 GHz.

InP/InGaAs photodetector based on a high electron mobility transistor layer structure: Its response at 1.3 μm wavelength

We report on the investigation of the room-temperature optoelectronic behavior of a metal–semiconductor–metal two-dimensional electron gas photodiode based on the two-dimensional electron gas of a high electron mobility transistor structure. The photodetector is fabricated in the InP/InGaAs material system, without use of Al-containing layers. Optoelectronic measurements on a device with a finger spacing of 3 μm show a full width at half-maximum (FWHM) of the pulse response of ≤60 ps, which is the resolution limit of our measurement equipment. Low-temperature measurements at 40 K with electro-optical sampling at a wavelength of 890 nm show a FWHM of 1 ps.

Optimizing n+ Ohmic Contacts on GaAs for HemtS

ABSTRACTLow ohmic contact resistance is essential for high performance microwave and millimeter wave transistors. Rapid thermal processing (RTP) has been used to optimize the ohmic contact resistance of gold - germanium / nickel / gold metallizations on gallium arsenide (GaAs) layers for high electron mobility transistor (HEMT) applications. A HEMT layer structure consisting of a 9000Å buffer layer grown on a semi-insulating substrate followed by a 20Å undoped AlGaAs spacer layer, a 700Å Al0.22Ga0.78 As layer doped at 1.0 × 1018cm-3and a 500Å GaAs cap layer doped at 1.5 × 1018 cm°C to 450°C. Time at temperature was varied from 10 seconds to 1 minute. Optimum conditions for our equipment and layer structure were found to be 365°C for 30 seconds. These conditions produced contact resistances of 0.08 ohm-mm (approximately 2.0 times better than the standard furnace alloy process).

Growth condition studies of pseudomorphic InGaAs/GaAs strained layer structures and InGaAs/AlGaAs high electron mobility transistor layer properties

We use reflection high-energy electron diffraction (RHEED) oscillations to study the growth condition dependence of the growth of pseudomorphic InGaAs layers on GaAs, as well as van der Pauw/Hall measurements to evaluate the growth parameter dependence of the electrical properties of InGaAs/AlGaAs high electron mobility transistor structures. We present our conclusions regarding growth conditions for which smooth RHEED oscillations can be obtained, and the parameters for which optimal electrical properties can be reached.