James M. Ballingall

DC and microwave characteristics of sub-0.1- mu m gate-length planar-doped pseudomorphic HEMTs

Analytical modeling of these very-short-channel HEMTs (high-electron-mobility transistors) using the charge-control model is given. The calculations performed using this model indicate a very high electron velocity in the device channel (3.2+or-0.2*10/sup 7/ cm/s) and clearly demonstrate the advantages of the planar-doped devices as compared to the conventional uniformly doped HEMTs. Devices with different air-bridged geometries have been fabricated to study the effect of the gate resistance on the sub-0.1- mu m HEMT performance. With reduced gate resistance in the air-bridge-drain device, noise figures as low as 0.7 and 1.9 dB were measured at 18 and 60 GHz, respectively. Maximum available gains as high as 13.0 dB at 60 GHz and 9.2 dB at 92 GHz, corresponding to an f/sub max/ of 270 GHz, have also been measured in the device. Using the planar-doped pseudomorphic structure with a high gate aspect-ratio design, a noise figure of less than 2.0 dB at 94 GHz is projected based on expected further reduction in the parasitic gate and source resistances. >

Very high power-added efficiency and low-noise 0.15- mu m gate-length pseudomorphic HEMTs

0.15- mu m-gate-length double-heterojunction pseudomorphic high electron mobility transistors (HEMTs) for which excellent millimeter-wave power and noise performance were achieved simultaneously are reported. The 50- mu m-wide HEMTs yielded record maximum power-added efficiencies of 51, 41, and 23% at 35, 60, and 94 GHz, respectively. Maximum output powers of 139 mW at 60 GHz and 57 mW at 94 GHz were also measured for 150- mu m-gate-width devices. Finally, minimum noise figures as low as 0.55 and 1.8 dB were measured at 18 and 60 GHz respectively. This is the best power and noise performance yet reported for passivated transistors at millimeter-wave frequencies.<<ETX>>

Low-frequency noise behavior of 0.15- mu m gate-length lattice-matched and lattice-mismatched MODFETs on InP substrates

Experimental data are presented on equivalent gate noise voltage from 1 to 10/sup 5/ Hz obtained from lattice-matched and strained InGaAs quantum-well modulation-doped field effect transistors (MODFETs). In both types of devices excess generation-recombination (g-r) noise is observed at or below 100 Hz above an apparent background 1/f noise with spectral intensity ranging from 0.5*10/sup -17/ to 2*10/sup -17/ V/sup 2/-Hz/sup -1/-cm/sup 2/ at 1 Hz. These results are comparable to those reported by S.M.J. Liu et al. (1986) for the pseudomorphic MODFETs.<<ETX>>

Sensitive optical gating of reverse-biased AlGaAs/GaAs optothyristors for pulsed power switching applications

A heterojunction-based optothyristor has been fabricated and tested with biasing field intensity up to 34 kV/cm for pulsed power applications. The reverse-biased optothyristor can even be triggered by a light-emitting diode (LED) of a few microwatts power, and more than 500 times reduction in the required LED power for triggering has been observed when compared to bulk photoconductive switches. The optothyristor, however, does not turn on under similar triggering conditions if bias polarity is changed. The sensitive optical gating of the reverse-biased optothyristor is explained. The turn-on delay time under reverse bias has been found to be inversely proportional to the square root of the LED power. The possibility of improving the switching efficiency by superimposing the laser pulse on a constant lower level background illumination has been demonstrated. >

Dynamic I-V characteristics of an AlGaAs/GaAs-based optothyristor for pulsed power-switching applications

A high-performance MBE-grown AlGaAs/GaAs-based heterostructure optothyristor has been fabricated and characterized for high-power pulsed switching applications. An LEC undoped semi-insulating GaAs of 650 mu m in thickness was used as the voltage blocking layer and low-temperature GaAs grown at 200 degrees C was used to passivate the surface and to reduce the surface leakage current. The dynamic current-voltage characteristics have been measured up to 115 A and 1974 V, which corresponds to a field intensity of more than 30 kV/cm. The dissipated energy per switching as a function of device voltage has also been determined to be in the range of 2 mJ or lower.<<ETX>>

A novel high power optothyristor based on AlGaAs/GaAs for pulsed power-switching applications

Double-side molecular beam epitaxial growth on a thick LEC-grown semi-insulating (SI) GaAs wafer has been used to demonstrate a novel high power optothyristor for pulsed power-switching applications. The optothyristor has a P/sup +/N-SI-PN/sup +/ thyristor-like structure with the capital P and N standing for the wider bandgap optical window material, AlGaAs, and the SI standing for a 650 /spl mu/m SI-GaAs substrate. With the insertion of the SI-GaAs bulk material into the conventional P/sup +/NPN/sup +/ thyristor structure and the use of wider bandgap AlGaAs, the device has achieved a record high performance compared to the existing GaAs or AlGaAs/GaAs based epitaxial thyristors. The performance of the optothyristors under forward bias has been characterized, including 1) the low field dynamic current-voltage characteristics to show post-triggering carrier injections. 2) the switched-current waveforms with varying device blocking voltage and from which the turn-on speed di/dt is determined, and 3) the dependence of the switched-current amplitude on the laser triggering position. >