Abdul Manaf Hashim

Large Modulation of Conductance in Interdigital-Gated HEMT Devices Due to Surface Plasma Wave Interactions

To investigate the presence of interactions between surface plasma waves of carriers in a two-dimensional electron gas (2DEG) at AlGaAs/GaAs heterostructure and electromagnetic space harmonic slow waves, interdigital-gated high-electron-mobility transistor (HEMT) devices were fabricated, and their input admittances were measured in the microwave region of 1–15 GHz. A large modulation of conductance, more than 1000 mS/mm, was observed. The conductance modulation was controlled by a drain-source voltage and showed a peak at a certain frequency whose position could be controlled by changing the pitch of the interdigital gates. The observed conductance and capacitance characteristics were in good agreement with the transverse magnetic (TM) mode analysis taking into account a nonuniform field distribution along the 2DEG channel. The result seems to prove the existence of surface plasma wave interactions even under the strongly collision-dominant situation in the microwave region and provides great hope for increased interactions at THz frequencies under nearly collision-free conditions.

Design, Fabrication and Characterization of GaAs‐Based Interdigital‐Gated HEMT Devices for Solid‐State THz Wave Amplifiers

Theoretical analysis of potential distribution in the interdigital‐gated high electron mobility transistor (HEMT) plasma wave device was carried out. The dc I–V characteristics of capacitively coupled interdigital structure showed that uniformity of electric field under the interdigital gates was improved compared to the dc connected interdigital gate structure. Admittance measurements of capacitively coupled interdigital gate structure in the microwave region of 10–40 GHz showed the conductance modulation by drain‐source voltage. These results indicate the existence of plasma wave interactions.

Odd Harmonic Responses in Two‐Dimensional AlGaAs/GaAs HEMT Devices Due to Plasma Wave Interaction

Plasma waves are oscillations of electron density in time and space, and in deep submicron field effect transistors, typical plasma frequencies, ωp, lie in the terahertz (THz) range and do not involve any quantum transitions. Hence, using plasma wave excitation for detection and/or generation of THz oscillations is a very promising approach. In this paper, the investigation of plasma wave interaction between the plasma waves propagating in a short‐channel High‐Electron‐Mobility Transistor (HEMT) and the radiated electromagnetic waves was carried out. Experimentally, we have demonstrated the detection of the terahertz (THz) radiation by an AlGaAs/GaAs HEMT up to third harmonic at room temperature and their resonant responses show very good agreement with the calculated results.

Analysis of Interactions between Drifting Plasma Waves in 2DEG Semiconductors and Electromagnetic Space Harmonic Waves using Three‐Dimensional Transverse Magnetic Mode Method

A theoretical three‐dimensional transverse magnetic (TM) mode analysis to describe the presence of interactions between surface plasma waves of carriers in a two‐dimensional electron gas (2DEG) at AlGaAs/GaAs heterostructure and electromagnetic space harmonics slow waves using the so‐called interdigital‐gated high‐electron‐mobility‐transistor (HEMT) plasma wave devices is presented. First, the device structure and the outline of theoretical formulation to determine the admittance of the interdigital structure are described. Then, the analysis of the space harmonics propagating through the interdigital slow‐wave structures is performed. Next, the numerical procedures to solve the integral equations which are used in determining the admittance are explained. Finally, we point out and discuss the main results of the theoretical analysis where an appearance of negative conductance is obtained.

Modeling and Characterization of Capacitively Coupled Interdigital-Gated HEMT Plasma Device for Terahertz Wave Amplification

A capacitively coupled interdigital-gated HEMT structure was used to investigate the occurrence of uniformity of electric field distribution along the structure. The structure was designed and simulated using Commercial Electromagnetic Sonnet Suites software. The return loss characteristics were analyzed and evaluated. The comparison of the admittance characteristics from simulation between dc connected structure and capacitively coupled structure is carried out in order to evaluate electromagnetic wave propagation. This structure kept uniform electric field in the channel when the dc biased is applied to the interdigital gate, which modulates the potential in the channel.

Basic Study of Plasma Wave Interactions in GaAs Interdigital- Gated HEMT Devices from Microwave up to THz Frequencies

The purpose of this paper is to investigate theoretically and experimentally possible interactions between the surface plasma wave in drifting carriers in 2D electron gas (2DEG) and electromagnetic space harmonics in a GaAs interdigital-gated HEMT device from microwave to THz frequencies