Giuseppe Moschetti

Sb-HEMT: Toward 100-mV Cryogenic Electronics

In this paper, we present a first full set of characteristics (dc, fT, fmax, and noise) of InAs/AlSb high-electron mobility transistors (HEMTs) operating under cryogenic temperature and low-power conditions. Those results are systematically compared and deeply analyzed at room temperature and 77 K. The characteristics improvement achieved at 77 K open up the possibility to develop ultralow-power cryogenic electronics (low-noise amplifier), featuring excellent high-frequency/noise performances below 100-mV dc biasing.

Anisotropic transport properties in InAs/AlSb heterostructures

We have investigated the anisotropic transport behavior of InAs/AlSb heterostructures grown on a (001) InP substrate. An electrical analysis showed anisotropic sheet resistance Rsh and electron mobility μn in the two dimensional electron gas (2DEG). Hall measurements demonstrated an enhanced anisotropy in μn when cooled from room temperature to 2 K. High electron mobility transistors exhibited 27% higher maximum drain current IDS and 23% higher peak transconductance gm when oriented along the [1-10] direction. The anisotropic transport behavior in the 2DEG was correlated with an asymmetric dislocation pattern observed in the surface morphology and by cross-sectional microscopy analysis of the InAs/AlSb heterostructure.

Cryogenic InAs/AlSb HEMT Wideband Low-Noise IF Amplifier for Ultra-Low-Power Applications

A cryogenic wideband 4-8 GHz hybrid low-noise amplifier, based on a 110 nm gate length InAs/AlSb HEMT process is presented. At room temperature the three-stage amplifier exhibited a transducer gain of 29 dB and a noise temperature of 150 K with 17.6 mW power consumption. When cooled to 13 K, the amplifier showed a minimum noise temperature of 19 K at a power consumption of 6 mW (66% reduction compared to room temperature). At cryogenic temperature, the optimum drain voltage for best noise performance was reduced from 0.55 V down to 0.3 V, demonstrating the very low-power and low-voltage capabilities of InAs/AlSb HEMT based low-noise amplifiers at cryogenic temperature.

Planar InAs/AlSb HEMTs With Ion-Implanted Isolation

The fabrication and performance of planar InAs/AlSb high-electron-mobility transistors (HEMTs) based on ion-implantation isolation technology are reported. Ar atoms have been implanted at an energy of 100 keV and with a dose of 2 ×1015 cm-2 in order to induce device isolation. The InAs/AlSb HEMT exhibited a maximum drain current of 900 mA/mm, a peak transconductance of 1180 mS/mm, and an fT/fmax ratio of 210 GHz/180 GHz at a low drain bias of 0.3 V. The combination of excellent stability against oxidation with the high device isolation demonstrated by the implantation technique can dramatically improve the suitability of InAs/AlSb HEMTs for high-frequency and ultralow-power MMIC applications.

Monte Carlo study of kink effect in Isolated-Gate InAs/AlSb High Electron Mobility Transistors

A semiclassical two-dimensional ensemble Monte Carlo simulator is used to perform a physical analysis of the kink effect in InAs/AlSb high electron mobility transistors (HEMTs). Kink effect, this is, an anomalous increase in the drain current I-D when increasing the drain-to-source voltage V-DS, leads to a reduction in the gain and a rise in the level of noise, thus limiting the utility of these devices for microwave applications. Due to the small band gap of InAs, InAs/AlSb HEMTs are very susceptible to suffer from impact ionization processes, with the subsequent hole transport through the structure, both implicated in the kink effect. The results indicate that, when V-DS is high enough for the onset of impact ionization, holes thus generated tend to pile up in the buffer (at the gate-drain side) due to the valence-band energy barrier between the buffer and the channel. Due to this accumulation of positive charge the channel is further opened and I-D increases, leading to the kink effect in the I-V characteristics and eventually to the device electrical breakdown. The understanding of this phenomenon provides useful information for the development of kink-effect-free InAs/AlSb HEMTs.

AlSb nucleation induced anisotropic electron mobility in AlSb/InAs heterostructures on GaAs

The influence of the growth conditions at the AlSb/GaAs interface on the electron mobility in AlSb/InAs heterostructures is investigated. We show that an excessive antimony flux during the initial stage of the AlSb buffer growth leads to a strong anisotropy of electron mobility in InAs between [110] and [1-10] crystallographic orientations. This anisotropy is attributed to the formation of trenches oriented along the [1-10] direction in the InAs channel. Transmission electron microscopy reveals that these trenches are directly related to twinning defects originating from the AlSb/GaAs interface.

Kink effect and noise performance in isolated-gate InAs/AlSb high electron mobility transistors

The kink effect can spoil the otherwise excellent low noise performance of InAs/AlSb high electron mobility transistors. It has its origin in the pile-up of holes (generated by impact ionization) taking place mainly at the drain side of the buffer, which leads to a reduction of the gate-induced channel depletion and results in a drain current enhancement. Our results indicate that the generation of holes by impact ionization and their further recombination lead to fluctuations in the charge of the hole pile-up, which provoke an important increase in the drain current noise, even when the kink effect is hardly perceptible in the output characteristics.

Dynamic Monte Carlo study of isolated-gate InAs/AlSb HEMTs

In this work, by means of Monte Carlo simulations, the static and dynamic behavior of isolated-gate InAs/AlSb high electron mobility transistors (Sb-HEMTs) has been studied and compared with experimental results. The influence of the existence of a native oxide under the gate, the value of the surface charges in the gate recess and the possible variation of electron sheet carrier density, n(s), have been studied. A decrease in the gate-source capacitance, transconductance and intrinsic cutoff frequency is observed because of the presence of the native oxide, while changes in the value of the surface charges in the recess only introduce a threshold voltage shift. The increase of n(s) shifts the maximum of the transconductance and intrinsic cutoff frequency to higher values of drain current and improves the agreement with the experimental results.

DC characteristics of InAs/AlSb HEMTs at cryogenic temperatures

The DC properties of 110-nm gate-length InAs/AlSb-based HEMTs at cryogenic (30K) and room temperature (300K) have been investigated. Compared to 300K, devices at 30 K exhibited lower on-resistance (R<inf>ON</inf>) and output conductance (g<inf>DS</inf>), a higher transconductance (g<inf>m</inf>) and a more distinct knee in the I<inf>DS</inf>(V<inf>DS</inf>) characteristics. The improvement in the DC performance at cryogenic temperature should mainly be attributed to the lower source-drain resistance.

Fabrication and DC characterization of InAs/AlSb self-switching diodes

Fabrication and DC measurements of an InAs/AlSb self-switching diode (SSD), aimed for THz detection, is presented. An SSD with a channel width of 160 nm and a trench width of 240 nm was designed and fabricated in a process using an in situ passivation procedure of the oxidation-sensitive trench. Rectifying behavior was observed in the I-V characteristics. The device performance was relatively stable over a period of three months.