Ludovic Desplanque

Terahertz frequency difference from vertically integrated low-temperature-grown GaAs photodetector

We report on the development of a photoconductive detector based on low-temperature-grown GaAs which is vertically integrated with terahertz spiral antennas. A non steady-state velocity overshoot effect was expected in the photoresponse with a responsivity of 0.04 A/W at a bias voltage of 8 V. Photomixing experiments using two optical 0.8 μm beating lasers show a 3 dB bandwith of 700 GHz with a radiation power at terahertz frequency of 0.5 μW under 2×30 mW optical pumping.

Electrical Characterization and Small-Signal Modeling of InAs/AlSb HEMTs for Low-Noise and High-Frequency Applications

Electrical characterization and modeling of 2 times 50 mum gatewidth InAs/AlSb HEMTs with 225 nm gate-length have been performed. The fabricated devices exhibited a transconductance gm of 650 mS/mm, an extrinsic cutoff frequency fT and an extrinsic maximum frequency of oscillation fmax of 120 and 90 GHz, respectively, already at a low VDS of 0.2 V. A minimum noise figure less than 1 dB between 2-18 GHz was achieved at a dc power consumption of only 10 mW/mm. This demonstrates the potential of InAs/AlSb HEMTs for low-power, low-noise applications. To account for the elevated gate-leakage current lG in the narrow-bandgap InAs/AlSb HEMT, the conventional field-effect transistor small-signal model has been extended. The relatively high IG was modeled by shunting both Cgs and Cgd with Rgs and .Rgd, respectively. As a result, the small-signal S-parameters were more accurately modeled, especially for frequencies below 10 GHz. Utilizing this modeling approach, excellent agreement was obtained between measured and modeled S-parameters, unilateral power gain U (Masons gain) and stability factor K.

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.

Terahertz detection in zero-bias InAs self-switching diodes at room temperature

RF characterization of InAs self-switching diodes (SSDs) is reported. On-wafer measurements revealed no roll-off in responsivity in the range of 2–315 GHz. At 50 GHz, a responsivity of 17 V/W and a noise-equivalent power (NEP) of 150 pW/Hz½ was observed for the SSD when driven by a 50 Ω source. With a conjugately matched source, a responsivity of 34 V/W and an NEP of 65 pW/Hz½ were estimated. An antenna-coupled SSD demonstrated a responsivity of 0.7 V/W at 600 GHz. The results demonstrate the feasibility of zero-bias terahertz detection with high-electron mobility InAs SSDs up to and beyond 100 GHz.

Gate-Recess Technology for InAs/AlSb HEMTs

The gate-recess technology for Si delta-doped InAs/AlSb high-electron-mobility transistors (HEMTs) has been investigated by combining atomic force microscopy (AFM) inspection of the gate-recess versus time with electrical device characterization. Deposition of the gate metal on the In0.5Al0.5As protection layer or on the underlying AlSb Schottky layer resulted in devices suffering from high gate-leakage current. Superior dc and high frequency device performance were obtained for HEMTs with an insulating layer between the gate and the Schottky layer resulting in a reduction of the gate leakage current IG by more than two orders of magnitude at a drain-to-source voltage VDS of 0.1 V. The existence of this intermediate insulating layer was evident from the electrical measurements. AFM measurements suggested that the insulating layer was due to a native oxidation of the AlSb Schottky layer. The insulated-gate HEMT with a gate length of 225 nm exhibited a maximum drain current ID higher than 500 mA/mm with good pinchoff characteristics, a dc transconductance gm of 1300 mS/mm, and extrinsic values for cutoff frequency fT and maximum frequency of oscillation fmax of 160 and 120 GHz, respectively.

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.

(Cl2:Ar) ICP/RIE Dry Etching of Al(Ga) Sb FOR AlSb/InAs HEMTs

Dry etching of AlSb and Al_0.80Ga_0.20Sb has been performed by inductively coupled plasma/reactive ion etching based on a (Cl₂:Ar) gas mixture without addition of BCI₃. The dry etch process has been used to fabricate AlSb/InAs high electron mobility transistors isolated by a shallow mesa. Good DC/RF results, with extrinsic f_T/f_max= 135/105 GHz, have been measured for a 2times50 mum HEMT with a gate length of 295 nm.

Influence of nanoscale faceting on the tunneling properties of near broken gap InAs/AlGaSb heterojunctions grown by selective area epitaxy

We report on the selective area molecular beam epitaxy of InAs/AlGaSb heterostructures on a GaSb (001) substrate. This method is used to realize Esaki tunnel diodes with a tunneling area down to 50 nm × 50 nm. The impact of the size reduction on the peak current density of the diode is investigated, and we show how the formation of the InAs facets can deeply affect the band-to-band tunneling properties of the heterostructure. This phenomenon is explained by the surface-dependent incorporation of Si dopant during growth.

On the effect of δ-doping in self-switching diodes

Lowering the carrier concentration is presented as a way to considerably improve the performance of self-switching diode (SSD) detectors. A physics-based theoretical model was used to derive an expression for the responsivity of SSDs as a function of carrier concentration, mobility, and design parameters. Monte Carlo simulations confirmed the modeled effect of varying carrier concentration and channel width. SSDs were fabricated in InAs heterostructures with different δ-doping levels. Radio frequency (RF) characterization at 50 GHz reproduced the modeled trends. By reducing the carrier concentration in InAs SSDs with 40 nm wide channels from 2.7 × 1012 cm−2 to 1.5 × 1012 cm−2 (−44%), the noise equivalent power (NEP) improved from 130 pW/Hz½ to 87 pW/Hz½ (−33%).