M. Arafa

Enhancement-mode high electron mobility transistors (E-HEMTs) lattice-matched to InP

The fabrication and characterization of high-speed enhancement-mode InAlAs/InGaAs/InP high electron mobility transistors (E-HEMTs) have been performed. The E-HEMT devices were made using a buried-Pt gate technology. Following a Pt/Ti/Pt/Au gate metal deposition, the devices were annealed in a nitrogen ambient, causing the bottom Pt layer to sink toward the channel. This penetration results in a positive shift in threshold voltage. The dc and RF performance of the devices has been investigated before and after the gate annealing process. In addition, the effect of the Pt penetration was investigated by fabricating two sets of devices, one with 25 nm of Pt as the bottom layer and the other with a 5.0 nm bottom Pt layer. E-HEMTs were fabricated with gate lengths ranging from 0.3 to 1.0 /spl mu/m. A maximum extrinsic transconductance (g/sub mext/) of 701 mS/mm and a threshold voltage (V/sub T/) of 167 mV was measured for 0.3 /spl mu/m gate length E-HEMTs. In addition, these same devices demonstrated excellent subthreshold characteristics as well as large off-state breakdown voltages of 12.5 V. A unity current-gain cutoff frequency (f/sub t/) of 116 GHz was measured as well as a maximum frequency of oscillation (f/sub max/) of 229 GHz for 0.3 /spl mu/m gate-length E-HEMTs.

High speed p-type SiGe modulation-doped field-effect transistors

We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-/spl mu/m and 1-/spl mu/m gate-lengths having unity current-gain cut-off frequencies (f/sub T/) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (g/sub m/) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-/spl mu/m gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few /spl mu/A/mm at room temperature and a few nA/mm at 77 K.

A 70-GHz f/sub T/ low operating bias self-aligned p-type SiGe MODFET

A self-aligned process for the fabrication of SiGe p-type modulation-doped field-effect transistors (MODFETs) is described. Self-aligned devices with 0.1-/spl mu/m gate-length have been fabricated and characterized. A maximum dc extrinsic transconductance of 258 mS/mm was obtained with a low turn-on resistance and very low knee voltage. Excellent high frequency performance with a unity current-gain cutoff frequency (f/sub T/) of 70 GHz was obtained. This excellent high frequency performance was exhibited even at drain bias as low as 0.5 V.

Fabrication and characterization of an InAlAs/InGaAs/InP ring oscillator using integrated enhancement- and depletion-mode high-electron mobility transistors

The fabrication and characterization of an 11-stage ring oscillator utilizing integrated enhancement- and depletion-mode (E/D-mode) high-electron mobility transistors (HEMTs) in the lattice-matched InAlAs/InGaAs/InGaAs material system is demonstrated. The 0.5-/spl mu/m gate length depletion-mode HEMTs (D-HEMTs) used in the circuit exhibit a threshold voltage (V/sub T/) of -365 mV with a standard deviation of 19 mV, while the enhancement-mode HEMTs (E-HEMTs) with identical gate length display a V/sub T/ of 195 mV with a standard deviation of only 9 mV. The unity current gain cutoff frequency (f/sub t/) for both devices is 70 GHz. The extremely high uniformity of the threshold voltages of these devices allowed for the implementation of a ring oscillator utilizing direct coupled FET logic (DCFL). At a supply voltage of 0.4 V, a room temperature propagation delay time (/spl tau//sub pd/) of 22.4 ps/stage, and a corresponding power dissipation of 120 /spl mu/W/stage is measured, yielding a power delay product (PDP) of 2.65 fJ/stage. To the best of the authors knowledge, this is the first demonstration of a circuit employing E/D-HEMT technology in the lattice-matched InP-based material system.

InGaAs metal-semiconductor-metal photodetectors with engineered Schottky barrier heights

An InAlAs/InGaAs/InP metal‐semiconductor‐metal photodetector with engineered Schottky barrier heights has been fabricated. A significant decrease in dark current with no change in the responsivity or the bandwidth was obtained by independently engineering the Schottky barrier heights at the anode and cathode. These photodiodes with an electrode width and spacing of 2 μm exhibited a dark current density of 20.0 fA/μm2 at an applied bias of 5 V. This dark current density is ∼6 times lower than the previously reported minimum.

DC and RF performance of 0.25 μm p-type SiGe MODFET

The DC and RF performance of a 0.25 /spl mu/m gate-length p-type SiGe modulation-doped field-effect transistor (MODFET) is reported. The hole channel consists of compressively strained Si/sub 0.3/Ge/sub 0.7/ layer grown on a relaxed Si/sub 0.7/Ge/sub 0.3/ buffer on a Si substrate. The combination of high-hole mobility, low-gate leakage current, and improved ohmic contact metallization results in an enhancement of the DC and RF performance. A maximum extrinsic transconductance (g(m/sub e/xt)) of 230 mS/mm was measured. A unity current gain cut-off frequency (fT) of 24 GHz and a maximum frequency of oscillation (f/sub max/) of 37 GHz were obtained for these devices.

Design, fabrication, and performance of high-speed monolithically integrated InAlAs/InGaAs/InP MSM/HEMT photoreceivers

A detailed study of the performance of monolithically integrated photoreceivers based on metal-semiconductor-metal (MSM) photodetectors (PDs) and HEMTs is undertaken. Two different stacked-layer approaches to integrating MSM-PDs with HEMTs are investigated, and the performance of detectors and HEMTs for each approach is compared. The structure with the MSM layers grown on top of the HEMT layers exhibited the best overall performance. A physics-based MSM model is developed and incorporated into microwave circuit design software; excellent agreement between circuit simulations and measured frequency responses is demonstrated. To evaluate the effects of MSM electrode geometry and detector area on photoreceiver performance, photoreceivers with MSM interelectrode spacings of 1, 1.5, and 2 /spl mu/m were fabricated and characterized. The electrical amplifier used in the photoreceivers is a two-stage, variable-transimpedance amplifier with a common-gate HEMT as the feedback path. By adjusting the DC voltage applied to the gate of this feedback HEMT, transimpedances ranging from 55.8 to 38.1 dB/spl Omega/, with corresponding -3 dB cutoff frequencies from 6.3 to 18.5 GHz, were measured experimentally. Excellent noise performance has been measured, with average input noise current spectral densities of 7.5, 8, and 12 pA/Hz/sup 1/2/ obtained for bandwidths of 6.3, 8, and 13.7 GHz, respectively. A packaged receiver has been tested at 5 Gb/s and an open eye pattern obtained.

Integrated enhancement- and depletion-mode FET's in modulation-doped Si/SiGe heterostructures

We present results of enhancement and depletion mode transistors fabricated on the same layer structure of Si/SiGe, without using gate recess. The current in the enhancement mode device is controlled by a p-n junction, while that of the depletion-mode device is controlled by a Schottky barrier. A peak transconductance of 327 mS/mm and 417 mS/mm has been achieved in 0.5-/spl mu/m gate length depletion and enhancement-mode transistors, respectively.

Submicrometer p-type SiGe modulation-doped field-effect transistors for high speed applications

Abstract Excellent improvement in the hole transport properties for SiGe heterostructures promises symmetric, higher speed, and lower power consumption circuits compared to conventional Si CMOS devices. Modulation-doped field effect transistors (MODFETs) grown on a relaxed Si 0.7 Ge 0.3 buffer have been fabricated using a self-aligned gate process. The p-type devices had gate lengths ranging from 1.0 μm down to 0.1 μm. A record unity current gain cutoff frequency f t of 70 GHz was obtained for 0.1 μm gate-length devices.

InGaAs metal-semiconductor-metal photodetectors with a hybrid combination of transparent and opaque electrodes

A metal-semiconductor-metal photodetector (MSMPD) with a hybrid combination of transparent cadmium-tin-oxide and opaque Ti:Au electrodes is proposed and demonstrated. A significant decrease in dark current is obtained by independently engineering the Schottky barrier heights at the anode and cathode. In addition, the use of transparent electrodes enables more light to be coupled into the front-side illuminated MSMPDs thereby increasing the responsivity. For an applied bias of 5 V, these devices exhibited an extremely low dark current density of 21.2 fA/μm2 and a high responsivity of 0.56 A/W to perpendicularly incident 1.31 μm wavelength light.