InP-based High Electron Mobility Transistors Research Articles

Equivalent small-signal model of InP-based HEMTs with accurate radiation effects characterization

In this paper, an effective equivalent modeling technique has been proposed to describe small-signal characteristics of InP-based high electron mobility transistors (HEMTs) after proton radiation, which is composed of an artificial neural network and equivalent-circuit models. Small-signal intrinsic parameters of InP-based HEMTs are extracted from S-parameters before and after 2 MeV proton radiation as modeling objects. The deep learning model of a generative adversarial network has been explored to expand the measured finite data samples. Four feedforward neural networks are incorporated to equivalent-circuit topology to form the equivalent model, which are trained to accurately predict the radiation-induced variations of Cgs, Cgd, Rds, and gm, respectively. The prediction accuracy of the developed equivalent model has been well verified in terms of the broad-band S-parameters under radiation fluence of 1 × 1014 and 5 × 1013 H+/cm2. This equivalent modeling method with characterization of radiation damage effects could provide significant guidance for the aerospace monolithic millimeter-wave integrated circuit design.

Performance Improvement by SiO₂ Hardmask in 100-nm InP-Based HEMTs for TMIC Applications

Benzocyclobutene (BCB) has been widely used as passivation and interlayer dielectric for sub-millimeter-wave applications and terahertz monolithic microwave integrated circuits (TMICs). In this work, the influence of BCB passivation on 100-nm InP-based high-electron-mobility transistors (HEMTs) was investigated. A set of 100-nm HEMTs with different gate recess structures were fabricated and compared. A SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{2}}$</tex-math> </inline-formula> hard mask was adopted in the gate recess, which contributed to an improved device performance after BCB passivation. DC and RF performances were characterized before and after BCB passivation. The results show that BCB passivation in the recess region degraded InP HEMTs’ performance, and a better performance was achieved by the SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{2}}$</tex-math> </inline-formula> hard mask. For traditional devices, of which the gate recess was exposed to silicon nitride (SiN <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{x}}\text{)}$</tex-math> </inline-formula> and BCB passivation layers, both dc and RF performances were deteriorated drastically even though the thickness of SiN <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula> passivation layer was increased from 20 to 50 nm. However, the SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{2}}$</tex-math> </inline-formula> hard mask preserved the device performances to a great degree, with only degradation by increased parasitic capacitances according to the small-signal equivalent model. In addition, the threshold voltage shift after BCB passivation was suppressed by the SiO <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{2}}$</tex-math> </inline-formula> hard mask. Thus, a device structure suitable for BCB passivated TMIC applications is proposed and validated.

Characterization of single event effect simulation in InP-based High Electron Mobility Transistors

The characteristics and mechanism of single event effects (SEEs) in InP-based High Electron Mobility Transistors (HEMTs) are investigated by technology computer-aided design (TCAD) simulations. The simulation results showed that the transient drain current became the highest after the heavy ion got incident in gate region, which means that the most sensitive location is gate region. With the increase of the linear energy transfer (LET) and drain voltage, the maximum drain current increases approximately linearly. The electric fields got increased with the increase of drain voltage, which led to the increase of the impact ionization rate, then producing more electron-hole pairs. Therefore, the drain current got increased with the increase of drain voltage. Moreover, the drain current become larger with the higher trap density, due to the higher electric field at drain. The thin thickness of InGaAs channel can significantly reduce SEE on the device. And the In mole fraction of InGaAs channel has a small effect on SEE.

Enhancement of f MAX of InP-based HEMTs by double-recessed offset gate process

A double-recessed offset gate process technology for InP-based high electron mobility transistors (HEMTs) has been developed in this paper. Single-recessed and double-recessed HEMTs with different gate offsets have been fabricated and characterized. Compared with single-recessed devices, the maximum drain–source current (I D,max) and maximum extrinsic transconductance (g m,max) of double-recessed devices decreased due to the increase in series resistances. However, in terms of RF performance, double-recessed HEMTs achieved higher maximum oscillation frequency (f MAX) by reducing drain output conductance (g ds) and drain to gate capacitance (C gd). In addition, further improvement of f MAX was observed by adjusting the gate offset of double-recessed devices. This can be explained by suppressing the ratio of C gd to source to gate capacitance (C gs) by extending drain-side recess length (L rd). Compared with the single-recessed HEMTs, the f MAX of double-recessed offset gate HEMTs was increased by about 20%.

Thermal annealing behavior of InP-based HEMT damaged by proton irradiation

In this paper, the effects of thermal annealing on the radiated InP-based high electron mobility transistors (HEMTs) is investigated. Proton irradiation is performed with energy of 2 MeV and fluence of 5 × 1013 cm−2, and subsequently the thermal annealing experiments are carried out at 100 ℃ and 200 ℃. Both drain-source saturation current (Id,sat) and maximum transconductance (gm,max) of the radiated devices demonstrate a certain degree of recovery after annealing at 100 ℃ and 200 ℃. Id,sat and gm,max recover by the maximum values of 17.37 % and 13.66% for 10 min annealing at 100 ℃, and 12.65% and 14.54% for 5 min thermal annealing at 200 ℃. The main reason for the recovery about the DC characteristics are the restore of carrier concentration and mobility. Thermal annealing has enhanced the atoms vibration, which decreases the concentration of defects by recombination and weakens the lattice scattering by rearranging the lattice. In addition, this paper reveals that different annealing temperature and duration will have different effects on irradiated InP-based HEMTs.

The effects and mechanisms of 2 MeV proton irradiation on InP-based high electron mobility transistors

InP-based high electron mobility transistors (HEMTs) are potential candidates for sub-millimeter wave and terahertz satellite communications due to their ultrahigh frequency performance. Therefore, the study of their irradiation reliability is extremely urgent. In this paper, a 2 MeV proton irradiation experiment has been carried out in InP-based HEMTs, and damage mechanisms have been systematically studied, including dc and rf characteristics. The experimental results show that InP-based HEMTs have wondrously excellent radiation tolerance. The degradation of electrical characteristics occurs only when the irradiation fluence is higher than 1 × 1013 H+/cm2. The drain saturation current and the maximum transconductance have, respectively, decreased by 7.1% and 5.4% at a fluence of 1 × 1014 H+/cm2. Different from the other III–V HEMTs, the irradiated InP-based HEMTs exhibited an abnormality in the “peak collapse” of transconductance. Rf characteristics' parameters demonstrate slighter degradation compared to dc transconductance. Transmission line model (TLM) measurement and Schottky barrier calculation have shown that there is no noticeable degradation of an Ohmic contact and a Schottky contact; therefore, the main possible reason for device degradation comes from the interior of a semiconductor structure. Furthermore, device simulation indicates that defects introduced by irradiation on the upper and lower heterojunction interface of the channel and the interface of the gate recess should be responsible for degradation. Our experiments show that InP-based HEMTs have excellent radiation resistance, and they have good prospects for applications in radiation environments.

Characterization of Single Event Effect Simulation in Inp-Based High Electron Mobility Transistors

Characterization of Single Event Effect Simulation in Inp-Based High Electron Mobility Transistors

Impact of gate offset in gate recess on DC and RF performance of InAlAs/InGaAs InP-based HEMTs

A set of 100-nm gate-length InP-based high electron mobility transistors (HEMTs) were designed and fabricated with different gate offsets in gate recess. A novel technology was proposed for independent definition of gate recess and T-shaped gate by electron beam lithography. DC and RF measurement was conducted. With the gate offset varying from drain side to source side, the maximum drain current (I ds,max) and transconductance (g m,max) increased. In the meantime, f T decreased while f max increased, and the highest f max of 1096 GHz was obtained. It can be explained by the increase of gate–source capacitance and the decrease of gate–drain capacitance and source resistance. Output conductance was also suppressed by gate offset toward source side. This provides simple and flexible device parameter selection for HEMTs of different usages.

A study of gate recess-width control of InP-based HEMTs by a Si3N4 passivation layer

Recess process for opening a narrow trench in the capping layer for T-shaped gates is one of the most important steps in the fabrication of InP-InAlAs/InGaAs based high electron mobility transistors, since the recessed-width strongly influences the DC/RF performances of the devices. Conventional chemical wet etch fails to well control the recess-width and its uniformity, leaving the seemingly small issue still rarely addressed so far. This work quantitatively analyzed the relationship between the recess-width and the DC/RF properties of the device by numerical simulations. To enhance the controllability of the recess-width, a 20-nm thick Si3N4 passivation layer pre-grown on the top of the capping layer was proposed. Careful comparisons of the recess-width as well as the device property with and without the passivation layer was carried out. Our results from both experiments and simulations indicate that it is promisingly feasible to control the recess-width to the desired scale by chemical wet etch when a dielectric layer such as Si3N4 is applied to protect the InGaAs capping layer from being over recessed, leading to enhanced device performance. With such an additional Si3N4 passivation layer, it is expected that the manufacturing yield of the InP-based high electron mobility transistors should be significantly enhanced with improved device performances.

Electron radiation impact on the kink effect in S 22 of InP-based high electron mobility transistors

In this paper, the effect of 1 MeV electron radiation on the kink effect in S 22 of InP-based high electron mobility transistors (HEMTs) has been comprehensively analyzed. The radiated fluence is varied among 1 × 1014 cm−2, 1 × 1015 cm−2 and 1 × 1016 cm−2. The size change of the kink effect before and after radiation is expressed by self-normalization and standard deviation. The results show that the kink effect appears at 36 GHz and becomes distinct in the sub-threshold region. The non-monotonous trend of the S 22 curve caused by the kink effect increases as the fluence increases. The dual-feedback circuit methodology is adopted to explain the influence of electron radiation on the kink effect; moreover, the change of transconductance and gate capacitance is the main reason for the influence of electron radiation on the kink effect in S 22. This research will provide theoretical guidance for InP-based HEMTs to be used in space radiation applications.

Influences of increasing gate stem height on DC and RF performances of InAlAs/InGaAs InP-based HEMTs* *Project supported by the National Natural Science Foundation of China (Grant No. 61434006).

The T-gate stem height of InAlAs/InGaAs InP-based high electron mobility transistor (HEMT) is increased from 165 nm to 250 nm. The influences of increasing the gate stem height on the direct current (DC) and radio frequency (RF) performances of device are investigated. A 120-nm-long gate, 250-nm-high gate stem device exhibits a higher threshold voltage (V th) of 60 mV than a 120-nm-long gate devices with a short gate stem, caused by more Pt distributions on the gate foot edges of the high Ti/Pt/Au gate. The Pt distribution in Schottky contact metal is found to increase with the gate stem height or the gate length increasing, and thus enhancing the Schottky barrier height and expanding the gate length, which can be due to the increased internal tensile stress of Pt. The more Pt distributions for the high gate stem device also lead to more obvious Pt sinking, which reduces the distance between the gate and the InGaAs channel so that the transconductance (g m) of the high gate stem device is 70 mS/mm larger than that of the short stem device. As for the RF performances, the gate extrinsic parasitic capacitance decreases and the intrinsic transconductance increases after the gate stem height has been increased, so the RF performances of device are obviously improved. The high gate stem device yields a maximum f t of 270 GHz and f max of 460 GHz, while the short gate stem device has a maximum f t of 240 GHz and the f max of 370 GHz.

Degradation mechanisms of InP-based high-electron-mobility transistors under 1 MeV electron irradiation

In this paper, InP-based high electron mobility transistors were investigated for an electron fluence of 5 × 1015 cm−2 at 1 MeV. The channel current and transconductance were reduced by 7.8% and 12.6% after electron irradiation. Meanwhile, the ION/IOFF ratio was reduced from 2.47 × 1012 to 2.16 × 102 and the SS was increased from 116.8 m mV dec−1 to 125.9 mV dec−1 after electron irradiation. To understand the degeneration behavior, the carrier concentration and mobility were calculated by the charge control model. Unlike, previous studies on the degradation behavior upon irradiation, the results show that these changes could only be attributed to the reduction of mobility in the channel by the irradiation-induced defects. The AFM and pulsed I–V curves measurement results proved that the Coulomb scatter effect was increased after electron irradiation, which led to decrease the carrier mobility. Besides, the current gain cut-off frequency (f T) was reduced from 139.4 GHz to 125.5 GHz and maximum oscillation frequency (f max) was reduced from 226.2 GHz to 206.1 GHz after electron irradiation. The degradation of frequency properties was mainly due to the increase of gate-drain capacitance and the channel resistance.

Enhancement of radiation hardness of InP-based HEMT with double Si-doped plane**Project supported by the National Natural Science Foundation of China (Grant Nos. 11775191, 61404115, 61434006, and 11475256) and the Promotion Funding for Excellent Young Backbone Teacher of Henan Province, China (Grant No. 2019GGJS017).

An anti-radiation structure of InP-based high electron mobility transistor (HEMT) has been proposed and optimized with double Si-doped planes. The additional Si-doped plane under channel layer has made a huge promotion in channel current, transconductance, current gain cut-off frequency, and maximum oscillation frequency of InP-based HEMTs. Moreover, direct current (DC) and radio frequency (RF) characteristic properties and their reduction rates have been compared in detail between single Si-doped and double Si-doped structures after 75-keV proton irradiation with dose of 5 × 1011 cm−2, 1 × 1012 cm−2, and 5 × 1012 cm−2. DC and RF characteristics for both structures are observed to decrease gradually as irradiation dose rises, which particularly show a drastic drop at dose of 5 × 1012 cm−2. Besides, characteristic degradation degree of the double Si-doped structure is significantly lower than that of the single Si-doped structure, especially at large proton irradiation dose. The enhancement of proton radiation tolerance by the insertion of another Si-doped plane could be accounted for the tremendously increased native carriers, which are bound to weaken substantially the carrier removal effect by irradiation-induced defects.

Feasibility Study of Wafer-Level Backside Process for InP-Based ICs

This paper reports wafer-level backside process technology, established with the intent to ensure stable operation of InP ICs in the submillimeter wavelength band, which generally suffer from ground bounce and substrate resonance. Our process consists of thinning a 3-in InP wafer, forming dense vias with interval cooling steps, backside metallization with single-level wiring and crack-free dicing. We investigate the effects of the backside process on InP-based heterojunction bipolar transistors and high electron mobility transistors. The results show that the backside process contributes to stable operation up to the 300-GHz range without any degradation of transistor characteristics.

Effect of Electron Irradiation Fluence on InP-Based High Electron Mobility Transistors.

In this paper, the effect of electron irradiation fluence on direct current (DC) and radio frequency (RF) of InP-based high electron mobility transistors (HEMTs) was investigated comprehensively. The devices were exposed to a 1 MeV electron beam with varied irradiation fluences from 1 × 1014 cm−2, 1 × 1015 cm−2, to 1 × 1016 cm−2. Both the channel current and transconductance dramatically decreased as the irradiation fluence rose up to 1 × 1016 cm−2, whereas the specific channel on-resistance (Ron) exhibited an apparent increasing trend. These changes could be responsible for the reduction of mobility in the channel by the irradiation-induced trap charges. However, the kink effect became weaker with the increase of the electron fluence. Additionally, the current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) demonstrated a slightly downward trend as the irradiation fluence rose up to 1 × 1016 cm−2. The degradation of frequency properties was mainly due to the increase of gate-drain capacitance (CGD) and the ratio of gate-drain capacitance and gate-source capacitance (CGD/CGS). Moreover, the increase of Ron may be another important factor for fmax reduction.

Effect of defects properties on InP-based high electron mobility transistors**Project supported by the National Natural Science Foundation of China (Grant Nos. 11775191, 61404115, 61434006, and 11475256), the Development Fund for Outstanding Young Teachers in Zhengzhou University of China (Grant No. 1521317004), and the Doctoral Student Overseas Study Program of Zhengzhou University, China.

The performance damage mechanism of InP-based high electron mobility transistors (HEMTs) after proton irradiation has been investigated comprehensively through induced defects. The effects of the defect type, defect energy level with respect to conduction band ET, and defect concentration on the transfer and output characteristics of the device are discussed based on hydrodynamic model and Shockley–Read–Hall recombination model. The results indicate that only acceptor-like defects have a significant influence on device operation. Meanwhile, as defect energy level ET shifts away from conduction band, the drain current decreases gradually and finally reaches a saturation value with ET above 0.5 eV. This can be attributed to the fact that at sufficient deep level, acceptor-type defects could not be ionized any more. Additionally, the drain current and transconductance degrade more severely with larger acceptor concentration. These changes of the electrical characteristics with proton radiation could be accounted for by the electron density reduction in the channel region from induced acceptor-like defects.

A theoretical study of gating effect on InP-InGaAs HEMTs by tri-layer T–shape gate

To maintain fast development of communication toward terrahertz frequencies, InP-based high electron mobility transistors in InGaAs/InAlAs heterojunctions with ultra-short T-shape gates are constantly demanded. Our earlier work has successfully developed a 10 nm wide T-shape gate anchored by a Si3N4 sheath for high mechanical reliability, nicknamed as the tri-layer T-shape gate. However, the short channel effect, the gating efficiency and the sheath effect on the device performance based on this gate structure are still unclear. This work focuses on the above mentioned issues, trying to establish the connection between the gate structure and the device DC/AC performance through systematic simulation study. The simulation results show that the tri-layer T-shape gate not only enhances the mechanical reliability, but also reduces the lateral electric field around the gate-edges, leading to high break down voltage. Furthermore, such a gate structure exhibits an improved gating efficiency with a positive threshold voltage (Vth) for the gate-width down to 50 nm. The only drawback with the existence of the sheath is that the operation frequency is reduced by 17% comparing to the conventional T shape gate. However, as high as 550 GHz for the current cut-off frequency is still feasible, which is much higher than that with the Si3N4 passivation field plate gate. The foundation built in this work is extremely imperative to the advances of THz technology.

Two-dimensional electron gas characteristics of InP-based high electron mobility transistor terahertz detector**Project supported by the Foundation for Scientific Instrument and Equipment Development, Chinese Academy of Sciences (Grant No. YJKYYQ20170032) and the National Natural Science Foundation of China (Grant No. 61435012).

The samples of two-dimensional electron gas (2DEG) are grown by molecular beam epitaxy (MBE). In the sample preparation process, the In content and spacer layer thickness are changed and two kinds of methods, i.e., contrast body doping and δ-doping are used. The samples are analyzed by the Hall measurements at 300 K and 77 K. The 2DEG channel structures with mobilities as high as (300 K) and (77 K) are obtained, and the values of carrier concentration (Nc) are 3.465×1012/cm2 and 2.502×1012/cm2, respectively. The THz response rates of InP-based high electron mobility transistor (HEMT) structures with different gate lengths at 300 K and 77 K temperatures are calculated based on the shallow water wave instability theory. The results provide a reference for the research and preparation of InP-based HEMT THz detectors.

Effects of proton irradiation at different incident angles on InAlAs/InGaAs InP-based HEMTs**Project supported by the National Natural Science Foundation of China (Grant Nos. 11775191, 61404115, 61434006, and 11475256), the Program for Innovative Research Team (in Science and Technology) in University of Henan Province, China (Grant No. 18IRTSTHN016), and the Development Fund for Outstanding Young Teachers in Zhengzhou University of China

InP-based high electron mobility transistors (HEMTs) will be affected by protons from different directions in space radiation applications. The proton irradiation effects on InAlAs/InGaAs hetero-junction structures of InP-based HEMTs are studied at incident angles ranging from 0 to 89.9° by SRIM software. With the increase of proton incident angle, the change trend of induced vacancy defects in the InAlAs/InGaAs hetero-junction region is consistent with the vacancy energy loss trend of incident protons. Namely, they both have shown an initial increase, followed by a decrease after incident angle has reached 30°. Besides, the average range and ultimate stopping positions of incident protons shift gradually from buffer layer to hetero-junction region, and then go up to gate metal. Finally, the electrical characteristics of InP-based HEMTs are investigated after proton irradiation at different incident angles by Sentaurus-TCAD. The induced vacancy defects are considered self-consistently through solving Poisson’s and current continuity equations. Consequently, the extrinsic transconductance, pinch-off voltage and channel current demonstrate the most serious degradation at the incident angle of 30°, which can be accounted for the most severe carrier sheet density reduction under this condition.

Si3N4/Al2O3 Stack Layer Passivation for InAlAs/InGaAs InP-Based HEMTs With Good DC and RF Performances

This paper introduces a novel surface passivation using Si3N4 (20-nm)/Al2O3 (15-nm) stack layers in InAlAs/InGaAs InP-based high-electron-mobility transistors (HEMTs). The new technology gives rise to good dc and RF performances in InP-based HEMTs. Notably different from the conventional Si3N4 approach, an ultrathin layer of Al2O3 (15-nm) grown by atomic layer deposition is incorporated in the surface passivation, which is the main feature of this technology. After passivation, the Si3N4/Al2O3-passivated HEMTs exhibit a superior dc performance demonstrating a high drain current up to 800 mA/mm, an increased peak transconductance of 1100 mS/mm at ${V} _{\mathrm{ GS}}=-0.2$ V and a slight threshold voltage shift of ${\Delta } {V} _{\mathrm{ th}}=+120$ mV. In terms of their RF performance, a maximum oscillation frequency ( ${f} _{\mathrm{ max}}$ ) up to 340 GHz has been obtained, showing an excellent quality of the surface passivation. A physical explanation is addressed over why the good dc and RF performances have been achieved.