GaAs Pseudomorphic High Electron Mobility Research Articles

A cryogenic GaAs PHEMT/ferroelectric Ku-band tunable oscillator

A Ku-band tunable oscillator operated at and below 77 K is described. The oscillator is based on two separate technologies: a 0.25 mm GaAs pseudomorphic high electron mobility transistor (PHEMT) circuit optimized for cryogenic operation, and a gold microstrip ring resonator patterned on a thin ferroelectric (SrTiO3) film which was laser ablated onto a LaAlO3 substrate. A tuning range of up to 3% of the center frequency was achieved by applying dc bias between the ring resonator and ground plane. To the best of our knowledge, this is the first tunable oscillator based on a thin film ferroelectric structure demonstrated in the microwave frequency range. The design methodology of the oscillator and the performance characteristics of the tunable resonator are described.

Transmission electron microscopy study of Si δ-doped GaAs/AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor structures

A high electron mobility transistor (HEMT) structure grown by molecular beam epitaxy consisting of a 2-nm In 0.3Ga 0.7As channel limited by a thick GaAs layer at the bottom and a 5-nm Al 0.3Ga 0.7As spacer at the top has been characterised by transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The carrier supplier of this structure is a Si δ-doped layer centred within a 1.7-nm wide GaAs quantum well grown on the spacer. (200) dark field (DF) TEM and HREM show well-defined InGaAs/GaAs and AlGaAs/InGaAs interfaces. The interface abruptness, the InGaAs layer thickness and its In composition have been quantitatively determined by strain measurements from 〈110〉 HREM images. The compositional profile obtained confirms an average InGaAs layer thickness of 7 group III monolayers (ML). All the layers are pseudomorphic, without dislocations or stacking faults. An inhomogeneous intensity distribution in DF TEM along the Si δ-doped GaAs layer suggests lateral Si segregation or strain modulation of which no evidence has been found by HREM. HREM reveals, however, an unusually large average lattice contraction at the position of the δ-doped layer which can be explained by atoms occupying non-lattice sites (DX centres).

High-gain frequency-tunable low-noise amplifiers for 38-42.5-GHz band applications

High-performance tunable low-noise amplifiers for 38-42.5 GHz applications are presented based on a fully stabilized GaAs pseudomorphic high electron mobility transistor (PHEMT) 0.2 μm technology. A single 1.5×3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> chip, incorporating six amplifying stages, shows a measured gain of 36-42 dB depending on the center frequency. Both maximum gain frequency and input impedance of the amplifier are accurately tunable on the chip. This means that the amplifier provides a narrow-band filtering function and can be matched to a fast p-i-n photodiode as well as to a 50 /spl Omega/ load. This is the first time such performances are reported for single chip narrow-band tunable amplifiers using a GaAs PHEMT technology.

Effects of O2 addition to SiCl4/SiF4 and the thickness of the capping layer on gate recess etching of GaAs-pseudomorphic high electron mobility transistors

The effects of the addition of a small amount of O2 to SiCl4/SiF4 plasma and the thickness of the GaAs capping layer on gate recess etching of GaAs pseudomorphic high electron mobility transistor (p-HEMT) devices have been studied. During gate recessing of GaAs/AlGaAs p-HEMTs using a selective reactive ion etching (RIE) process in SiCl4/SiF4 plasma [see S. K. Murad, N. I. Cameron, P. D. Wang, S. P. Beaumont, and C. D. W. Wilkinson, Microelectron. Eng. 27, 439 (1995)], it was found that the profile of the gate changes dramatically from undercut to nearly vertical with no lateral etching when the thickness of the capping layer was reduced below 40 nm. This vertical profile puts the gate metal too close to the recess edges in devices with a ≤30 nm capping layer. The addition of a very small amount of O2 to SiCl4/SiF4 plasma was seen to increase GaAs etch rates remarkably, while maintaining the high selectivity over AlGaAs. This increase in the etch rate agrees well with optical emission spectroscopic observations which indicate that the Cl emission has increased by more than an order of magnitude for the addition of only 1.5% of O2 to SiCl4/SiF4 plasma. This selective RIE process of SiCl4/SiF4/O2 was applied to gate recess etching of GaAs/AlGaAs/InGaAs p-HEMTs with various capping layer thicknesses. The profile of the T gates changed from nearly vertical (with no undercut or gate offset) to undercut with a lateral etch rate depending on the thickness of the capping layer. The lateral etching rate also strongly depends on the O2 flow. The p-HEMT devices gate recessed using this process (SiCl4/SiF4/O2) exhibited an ft of 120 GHz, gm of 700 mS/mm and a gain of 9.5 dB at 94 GHz.

Temperature dependence study of two-dimensional electron gas effect on the noise performance of high frequency field effect transistors

We present experimental evidence that the noise figure (NF) and associated gain equal to those achieved with GaAs pseudomorphic high electron mobility transistors (GaAs p-HEMT's) can also be accomplished by ion implanted GaAs metal-semiconductor field-effect transistors (GaAs MESFET's). These measured noise figure results as a function of low temperature for GaAs MESFET's and p-HEMT's clearly suggest that the transport properties of the two-dimensional electron gas in HEMT's and p-HEMT's do not make a significant contribution to the noise reduction at high frequency operation of these devices. >