T. Brock

375‐GHz‐bandwidth photoconductive detector

We report the development of a new, integrable photoconductive detector, based on low‐temperature‐grown GaAs, that has a response time of 1.2 ps and a 3‐dB bandwidth of 375 GHz. The responsivity is 0.1 A/W. Signal amplitudes up to 6 V can be produced with virtually no degradation in response time.

A D-band monolithic fundamental oscillator using InP-based HEMTs

The design and experimental characteristics of the first fundamental D-band monolithic high-electron-mobility transistor (HEMT) oscillator are reported. The circuit is based on a dual feedback topology and uses 0.1- mu m pseudomorphic double heterojunction InAIAs/In/sub 0.7/Ga/sub 0.3/As HEMTs. It includes on-chip bias circuitry and an integrated E-field probe for direct radiation into the waveguide. An oscillation frequency of 130.7 GHz was measured and the output power level was -7.0 dBm using HEMTs of small gate periphery (90 mu im). This represents the highest frequency of fundamental signal generation out of monolithic chips.<<ETX>>

Monolithically integrated InP-based front-end photoreceivers

The performance characteristics of a monolithically integrated front-end photoreceiver, consisting of a photodiode and a MODFET amplifier, were analyzed and measured. A vertical scheme of integration was initially used to realize a photoreceiver circuit on InP consisting of an InGaAs p-i-n diode, an InGaAs/InAlAs pseudomorphic MODFET, and passive circuit elements. The device structures were grown by single-step molecular beam epitaxy with an isolating layer in between. The microwave performance of 1- mu m-gate MODFETs in the circuit is characterized by f/sub T/=9 GHz, although identical discrete devices have f/sub T/=30-35 GHz. The degradation is due to additional parasitic capacitances present in this integration scheme. In spite of this disadvantage the bandwidth of the circuit is 2.1 GHz. Integration of the p-i-n diode with 1.0- and 0.25- mu m-gate MODFETs has also been done in a planar scheme using regrowth, and receiver bandwidths of 6.5 GHz were measured. This value is comparable to that of hybrid circuits with InP-based devices. >

Characteristics of InAs/AlGaAs self-organized quantum dot modulation doped field effect transistors

We have investigated the dc characteristics of InGaAs/AlGaAs modulation doped field effect transistors in which a layer of self-organized InAs quantum dots is inserted adjacent to the pseudomorphic quantum well channel. Distinct steps and a negative differential resistance are observed in the current–voltage characteristics at room temperature and lower temperatures. These are attributed to conduction through the bound states in the quantum dots.

Experimental characteristics and performance analysis of monolithic InP-based HEMT mixers at W-band

Experimental characteristics of monolithic InAlAs/InGaAs HEMT mixers are presented together with a theoretical analysis. Experiments at W-band show a maximum conversion gain of 0.9 dB with 2 dBm of LO power level. This is the first demonstration of a monolithic HEMT mixer with conversion gain at W-band. The conversion gain dependence on LO power, RF frequency and gate bias is measured and compared with the theoretical predictions. Good agreement between the theory and experiment could be found. >

Photoluminescence and electro‐optic properties of small (25–35 nm diameter) quantum boxes

The luminescence and electro‐optic properties of buried 25–35 nm quantum boxes have been measured. The quantum boxes were defined by a combination of molecular beam epitaxial growth and regrowth, electron beam lithography, and dry etching. The photoluminescence from 35 nm boxes shows a blue shift of ∼15 meV compared to the bulk luminescence and an enhancement, taking into account the fill factor. An enhanced effective linear electro‐optic coefficient, rl, is observed for the quantum boxes.

A D-band monolithic fundamental oscillator using InP-based HEMT's

The design, analysis and experimental characteristics of the first fundamental D-band monolithic high-electron-mobility transistor (HEMT) oscillator are reported. The circuit is based on a dual feedback topology and uses 0.1- mu m pseudomorphic double heterojunction InAlAs/In/sub 0.7/Ga/sub 0.3/As HEMTs. It includes on-chip bias circuitry and an integrated E-field probe for direct radiation into the waveguide. An oscillation frequency of 130.7 GHz was measured, and the output power level was -7.0 dBm using HEMTs of small gate periphery (90 mu m). This represents the highest frequency of fundamental signal generation out of monolithic chips using three-terminal devices. >

Characteristics of 0.8- and 0.2- mu m gate length In/sub x/Ga/sub 1-x/As/In/sub 0.52/Al/sub 0.48/As/InP (0.53<or=x<or=0.70) modulation-doped field-effect transistors at cryogenic temperatures

The performance characteristics of InP-based pseudomorphic MODFETs with varying the In composition (0.53 >

Experimental and theoretical characteristics of high performance pseudomorphic double heterojunction InAlAs/In/sub 0.7/Ga/sub 0.3/As/InAlAs HEMT's

Pseudomorphic double heterojunction (DH) InAlAs/In/sub 0.7/Ga/sub 0.3/As/InAlAs HEMTs with very high cut-off frequencies and current densities have been demonstrated. DC and microwave characteristics of the double heterojunction and single heterojunction (SB) HEMTs have been compared. Two identical layers except for the dopings have been grown and fabricated using a conventional non-self-aligned process for this purpose. In order to further enhance the performance level of DH-HEMTs, a sub-0.1 /spl mu/m offset /spl Gamma/-gate self-aligned process has been used on DH layers. A minimum frequency of oscillation (f/sub max/) of 350 GHz and a current gain cut-off frequency (f/sub T/) of 180 GHz have been achieved in this way along with the full channel current of 1.2 A/mm. Theoretical simulation using 2-D ensemble Monte Carlo simulation has also been performed to optimize the DH layer structure and to study the transport characteristics of DB-HEMTs compared with SH counterparts. >

W-band monolithic mixer using InAlAs/InGaAs HEMT

A W-band monolithic mixer is designed and fabricated using InAlAs/InGaAs HEMT technology. The advantages of this material system compared with AlGaAs/GaAs are: (i) larger conduction band discontinuity (0.5 eV versus 0.24 eV for AlGaAs/GaAs) and therefore better carrier confinement, (ii) higher low-field mobility, and (iii) higher peak velocity. The combination of these features results in a better performance and operation capability in the submillimeter wave range. The design procedure and the circuit performance are described. A very low LO (local oscillator) power requirement is demonstrated with 13.5-dB conversion loss and only -6 dBm LO drive at 95 GHz.<<ETX>>