Pseudomorphic HEMT Devices Research Articles

Quantitative strain and compositional studies of InxGa1-xAs Epilayer in a GaAs-based pHEMT device structure by TEM techniques.

In GaAs-based pseudomorphic high-electron mobility transistor device structures, strain and composition of the In x Ga1-x As channel layer are very important as they influence the electronic properties of these devices. In this context, transmission electron microscopy techniques such as (002) dark-field imaging, high-resolution transmission electron microscopy (HRTEM) imaging, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging and selected area diffraction, are useful. A quantitative comparative study using these techniques is relevant for assessing the merits and limitations of the respective techniques. In this article, we have investigated strain and composition of the In x Ga1-x As layer with the mentioned techniques and compared the results. The HRTEM images were investigated with strain state analysis. The indium content in this layer was quantified by HAADF imaging and correlated with STEM simulations. The studies showed that the In x Ga1-x As channel layer was pseudomorphically grown leading to tetragonal strain along the [001] growth direction and that the average indium content (x) in the epilayer is ~0.12. We found consistency in the results obtained using various methods of analysis.

High power density AlGaAs/InGaAs/GaAs PHEMTs using an optimised manufacturing process for Ka-band applications

In this study, a novel manufacturing process for a 0.1μm T-gate is investigated for producing a high output power performance for the Ka-band frequencies using high-quality AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors (PHEMTs) on semi-insulated (SI) GaAs substrates. The gate manufacturing process is the most important process due to its intimate relationship with the DC and RF performance of the device. To improve the gate performances of PHEMT devices, we investigated various materials and processing approaches involving a wide gate recess, double exposure by e-beam lithography, and low-damage double-gate passivation methods based on plasma-enhanced chemical vapour deposition (PECVD). To reduce the sensitivity to current collapse effects, we investigate the relationship between the electrical characteristics of the PHEMTs and top and bottom gate-supported passivation films. To improve the ohmic contact performance, we test an AuGe/Ni/Au (200/30/120nm) ohmic contact metallisation scheme using the rapid thermal annealing (RTA) process at temperatures ranging from 450°C 30s. A PHEMT with a gate length of 0.1μm, exhibiting a maximum drain current density of 680mA/mm, a peak transconductance of 500mS/mm, a unity-gain cut-off frequency (fT) of 56GHz, and a maximum frequency of oscillation (fMAX) of 84GHz, is demonstrated using this novel manufacturing process; the Ka-band power performance includes an output power density of 2.4W/mm and a power-added efficiency (PAE) of 44.6%.

Bias-dependent hybrid PKI empirical–neural model of microwave FETs

Empirical models of microwave transistors based on an equivalent circuit are valid for only one bias point. Bias-dependent analysis requires repeated extractions of the model parameters for each bias point. In order to make model bias-dependent, a new hybrid empirical–neural model of microwave field-effect transistors is proposed in this article. The model is a combination of an equivalent circuit model including noise developed for one bias point and two prior knowledge input artificial neural networks (PKI ANNs) aimed at introducing bias dependency of scattering (S) and noise parameters, respectively. The prior knowledge of the proposed ANNs involves the values of the S- and noise parameters obtained by the empirical model. The proposed hybrid model is valid in the whole range of bias conditions. Moreover, the proposed model provides better accuracy than the empirical model, which is illustrated by an appropriate modelling example of a pseudomorphic high-electron mobility transistor device.

On the Extension of the Continuous Class-F Mode Power Amplifier

The extended continuous class-F mode RF power amplifier (PA) is presented for the first time. The introduction and experimental validation of this novel PA mode demonstrates a new design space over a wide band of frequencies. This paper will show that high output power and drain efficiency, equivalent to the class-F mode, can be maintained by varying the reactive components of fundamental and second harmonic impedances in accordance with the new formulation of the voltage waveform. Additionally it will be shown that, by varying both phase and magnitude of the fundamental and second harmonic impedances, a yet wider design space can be achieved, where the efficiency is maintained at a level greater than a certain target value. For the validation of this new theory, an experimental investigation was carried out on GaAs pseudomorphic HEMT devices and demonstrates that high output power and drain efficiency between 75%-83% can be achieved over a wide range of fundamental and second harmonic loads.

Proposal of High-Electron Mobility Transistors With Strained InN Channel

By using a Schrödinger-Poisson equation solver, we calculate band diagrams of potentially record fast III-N high electron mobility transistors (HEMTs), which are based on strained InN channels. Assuming cation polarity, pseudomorphic HEMT devices are proposed with a relaxed InAIN buffer layer having Al mole fraction in the range of 0.10-0.15 and with an InAIN barrier layer. Calculations indicate highly confined electrons in the channel with a density of 1.4-2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> if the 5-10-nm-thick InN channel is separated from the barrier by ≤ 0.8-nm-thick GaN spacer. Alternatively, for a nonpolar structure with an Al mole fraction of 0.3 in the InAIN buffer and for a doping 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> in the InAIN barrier, we calculate the InN channel carrier density of approximately 1.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . We propose to use high-k dielectrics to insulate the gate from the barrier for both of the transistor structures.

Correlation between E 1 transition broadening and carrier mobility in the channel layer of pseudomorphic high electron mobility transistor epistructures

We present results from photoreflectance (PR) experiments conducted near the E1 transition energies (2.60–3.35 eV) of Al0.25Ga0.75As/In0.15Ga0.85As heterostructures that constitute the upper layers of pseudomorphic high electron mobility transistor (PHEMT) device epistructures. The lifetime broadening parameter (Γ) of the PR signal from the higher lying transition (E1) of InGaAs layer shows a strong correlation with the electron mobility. The E1 transition energies of the AlGaAs and InGaAs layers were used to determine the aluminum and indium mole fractions in the alloy. This study provides an insight into the correlation of a PR parameter with a carrier transport property and provides an alternate method to characterize the barrier and channel layers of PHEMT device structures. The results indicate the advantages of PR characterization employing higher lying transitions.

Coupled electrothermal, electromagnetic, and physical modeling of microwave power FETs

This paper presents a coupled electrothermal, electromagnetic, and physical model for microwave power field-effect transistors (FETs). The resulting model is used to investigate large gate periphery pseudomorphic high electron-mobility transistor devices. The contribution to the output power of each cell of the transistor is simulated, as well as their contribution to the heating of the device. This approach allows the investigation of the interaction between the thermal behavior, the dc bias, and the microwave circuit operating conditions. This paper reveals for the first time a more complex interaction between the thermal and microwave behavior of large-power FETs

Improved Y-factor method for wide-band on-wafer noise-parameter measurements

A new noise-figure measurement method, which combines the simplicity of the "classical" Y-factor method with the accuracy of the widely used "cold noise-source" method, is reported. Implemented in our fully automated wide-band 1-18-GHz on-wafer noise-parameter measurement system, accurate results are obtained using a small set of precharacterized source impedances. We illustrate our method and its accuracy with data taken on a low-noise GaAs pseudomorphic high electron-mobility transistor device, and quantify the impact of the instrumental uncertainties on the extracted noise parameters.

High reliability in PHEMT MMICs with dual-etch-stop AlAs layers for high-speed RF switch applications

We have conducted a thorough investigation on the long-term process reliability for our recently developed dual-etch-stop (DES) pseudomorphic high electron mobility transistor (PHEMT) process using the on-wafer-level accelerated DC and RF biased step stress test up to 320 °C channel temperature as well as package-level three-temperature constant stress lifetest. Devices studied are 0.9-μm-gate InGaAs PHEMTs with two silicon-doped AlAs layers as gate and channel etch-stop materials. High-temperature-operating-life (HTOL) test on our single-pole-double-throw (SPDT) switch products using this DES PHEMT process has also been performed. This article describes the detailed reliability experiments and compares the reliability results of this new DES PHEMT process against the standard non-etch-stop (NES) PHEMT baseline material. Extensive statistical analyses on the DES PHEMT devices derived an activation energy E a=1.4 eV and a mean-time-to-failure (MTTF) > 10 7 h at 125 °C, an order of magnitude better than our baseline NES PHEMTs. This study demonstrates and discusses the excellent reliability in the DES PHEMT process for wireless communications applications.

Direct extraction of FET noise models from noise figure measurements

An algorithm is presented that allows for noniterative extraction of the parameters of the Pucel and Pospieszalski FET noise models directly from noise-figure measurements. Since the goal is to minimize the number of source-pull measurements, the number of different source admittances required as a minimum to determine the model parameters reliably is investigated. It turns out that, in the case of the Pospieszalski model, 50-/spl Omega/ measurements are sufficient, while in case of the Pucel model, three additional source impedances have to be taken into account. The results are verified by investigating MESFET and pseudomorphic high electron-mobility transistor devices.

Using photoluminescence as optimization criterion to achieve high-quality InGaAs/AlGaAs pHEMT structure

The single δ-doped InGaAs/AlGaAs pseudomorphic HEMT structure materials were grown by molecular beam epitaxy. The photoluminescence spectra of the materials were studied. There are two peaks in the photoluminescence spectra of the materials, corresponding to two sub energy levels of InGaAs quantum well. The ratio of the two peak's intensity was used as criterion to optimize the layer structures of the materials. The material with optimized layer structures exhibits the 77 K mobility and two-dimensional electron gas density of 16 500 cm 2/V s and 2.58×10 12 cm −2 respectively, and the 300 K mobility and two-dimensional electron gas density of 6800 cm 2/V s and 2.55×10 12 cm −2 respectively. The pseudomorphic HEMT devices with gate length of 0.2 μm were fabricated using this material. The maximum transconductance of 650 mS/mm and the cut-off frequency of 81 GHz were achieved.

A robust integrated multibias parameter-extraction method for MESFET and HEMT models

An integrated multibias extraction technique for MESFET and high electron-mobility transistor (HEMT) models is presented in this paper. The technique uses S-parameters measured at various bias points in the active region to construct one optimization problem, of which the vector of unknowns contains a set of bias-dependent elements for each bias point and one set of bias-independent elements. This problem is solved by an extremely robust decomposition-based optimizer, which splits the problem into n subproblems, n being the number of unknowns. The optimizer consistently converges to the same solution from a wide range of randomly chosen starting values. No assumptions are made concerning the layout of the device or the bias dependencies of the intrinsic model elements. It is shown that there is a convergence in the values of the model elements and a decrease in the extraction uncertainty as the number of bias points in the extraction is increased. Robustness tests using 100 extractions, each using a different set of random starting values, are performed on measured S-parameters of a MESFET and pseudomorphic HEMT device. Results indicate that the extracted parameters typically vary by less than 1%. Extractions with up to 48 bias points were performed successfully, leading to the simultaneous determination of 342 model elements.

Power PHEMT with compact device layout forlow voltage CDMA application

A high efficiency low voltage operation dual delta-doped AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) for low voltage code division multiple access (CDMA) application has been developed. When tested at 2.4 V and 1.9 GHz under IS-95 CDMA modulation, the 20.16 mm PHEMT device was found to have a linear output power of 28 dBm with a power added efficiency of 30.2%. The device also has a saturation power of 30.0 dBm with a power added efficiency of 61.5%. The high efficiency and linearity of the PHEMT at low bias voltage is attributed to the use of the dual delta-doped PHEMT structure and to the reduction of the size of the device layout. The device is suitable for low voltage CDMA applications.

Molecular beam epitaxial growth and device performance of metamorphic high electron mobility transistor structures fabricated on GaAs substrates

Single and double pulse doped metamorphic high electron mobility transistor (MHEMT) structures have been grown on GaAs substrates by molecular beam epitaxy. A linear indium graded buffer layer was used to expand the lattice constant. Transmission electron microscopy cross sections showed planar interfaces. Threading dislocations were not observed along both cleavage directions. For a single pulse doped MHEMT structure with an In0.56Ga0.44As channel layer, the mobilities (10 030 cm2/V s at 292 K; 32 560 cm2/V s at 77 K) and sheet density (3.2×1012 cm−2) were nearly equivalent to values obtained for the same structure grown on an InP substrate. Secondary ion mass spectroscopy measurements of a double pulse doped structure indicated no measurable migration of the silicon doping pulses. MHEMT devices with 0.15 μm gates were fabricated, tested, and compared to GaAs pseudomorphic HEMT devices of the same geometries. Above 9 GHz, the MHEMT devices exhibited lower noise figure. From 3 to 26 GHz, the associated gain was 3 dB higher with the MHEMT devices. Also higher linearity performance was obtained with the MHEMT devices. At 4 GHz MHEMT linearity measurements yielded third order intermodulation distortion intercepts, IP3, of 36–39 dBm with linearity figure of merits of 60–90. Due to the significantly lower cost and more robustness of GaAs substrates compared to InP substrates, MHEMT technology is very promising for low cost manufacturing of low noise amplifiers.

Noise Performance of Pseudomorphic AlGaAs/InGaAs/GaAs High Electron Mobility Transistors with Wide Head T-Shaped Gate Recessed by Electron Cyclotron Resonance Plasma Etching

Passivated 0.15 µm pseudomorphic high electron mobility transistors (PHEMTs) were fabricated by combining a wide head T-shaped gate, formed using a dose split method of electron beam lithography, with a short source-gate separation, using formed an electron cyclotron resonance dry recess etching process. The threshold voltage of the devices showed 50 mV variation across three-inch wafers. The extrinsic transconductance and cutoff frequency of the PHEMT devices were 688 mS/mm and 82.6 GHz, respectively. The lowest minimum noise figure, NFmin, of the PHEMT devices was observed around 80% of the saturation drain current at 30 GHz and Vds = 2 V. The devices exhibited a NFmin as low as 0.99 dB with an associated gain of 9.1 dB at 30 GHz. This noise figure value is the lowest data ever reported for a PHEMT device using a dry recess process.

Enhanced Current-Voltage Characteristics of Al0.25Ga0.75As/In0.25Ga0.75As/GaAs P-HEMTs Using an Inverted Double Channel Structure

An inverted double channel Al0.25Ga0.75As/In0.25Ga0.75As/GaAs pseudomorphic high electron mobility transistor (P-HEMT) grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) has been demonstrated for the first time. The inverted double channel heterostructure shows a high two-dimensional electron gas (2-DEG) concentration of 4.53×1012 cm-2 along with a large mobility of 5010 cm2/V·s at 300 K, respectively. The fabricated P-HEMT device with a gate dimension of 1.8×200 µm2 shows a maximum drain current of as high as 820 mA/mm and a maximum extrinsic transconductance of 320 mS/mm at 300 K. Also, extrinsic transconductance is sustained over a wide range of gate voltages from -2.0 V to 1.8 V. In addition, a high two-terminal gate-drain reverse breakdown voltage of -17 V is obtained. The results obtained show a great potential of the inverted double channel P-HEMT for power applications.

A high-power and high-efficiency monolithic power amplifier at 28 GHz for LMDS applications

A high-power and high-efficiency monolithic power amplifier operating from 27.5 to 29.5 GHz is presented for local multipoint distribution service. Using 0.15-/spl mu/m InGaAs/AlGaAs/GaAs pseudomorphic high electron-mobility transistor devices, the two-stage power amplifier on 4-mil GaAs substrate demonstrated greater than 16-dB small-signal gain, 32-dBm (1.6 W) power with 35% power-added efficiency. The amplifier attained peak output power of 33.9 dBm (2.4 W) and peak power-added efficiency of 37%. At the peak power level, the amplifier exhibited power densities in excess of 640 mW/mm, which is the highest output power density attained by Ka-band monolithic power amplifiers. At lower drain voltage, the amplifier attained 43% power-added efficiency with 30-dBm output power.

Recessed-gate AlGaAs/InGaAs/GaAs pseudormorphicHEMTwith Si-planar-doped etch stop layer

An improved slot etch technique based on an Si planar doped layer has been applied to gate recessing in the fabrication of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors (HEMTs). The devices exhibited comparable gm with much better breakdown and leakage behaviour than conventional pseudomorphic HEMT devices.

Pseudomorphic HEMT Devices for Microwave and Millimeter Wave Applications

ABSTRACTPseudomorphic HEMT (PHEMT) devices have demonstrated superior performance at microwave and millimeter wave frequency ranges. They exhibit multi-functional characteristics such as high power, high efficiency and low noise over a broad frequency range (C-band through W-band). Because of their important, broad range of applications, the microwave industry has recently begun developing the PHEMT manufacturing technology in order to cope with the increasing demand for PHEMT insertion into microwave products. In this paper we will discuss the advantages of using PHEMT devices for microwave and millimeter wave applications and provide an overview of the published state-ofthe-art performance of PHEMT devices and monolithic microwave integrated circuits (MMICs) at microwave and millimeter wave frequencies. We will also present recent progress in Hughes PHEMT technology development including device epitaxial design and process enhancements. Finally, we will present recent data on PHEMT reliability.

Ultra-low-noise millimeter-wave pseudomorphic HEMTs

Pseudomorphic high-electron-mobility transistors (PHEMTs) with gate lengths of 0.1 mu m and based on the AlGaAs-InGaAs-GaAs material system are presented. The room-temperature device noise figure at 43 GHz is measured to be 1.32 dB (noise temperature=103 K) with 6.7 dB associated gain; when the device is cooled to 17 K, the noise figure falls to 0.36 dB (noise temperature=25 K) with 6.9 dB of associated gain. These pseudomorphic devices also show improved sensitivity to input noise match (N=0.13 at 43 GHz) compared with conventional HEMTs and MESFETs. These PHEMT devices have the lowest noise temperature and noise sensitivity (normalized to frequency) reported to date. >