Dee-Son Pan

Intersubband absorption of silicon-based quantum wells for infrared imaging

We have calculated the 10‐μm intersubband absorptoin in quantum wells made of the silicon‐based system, Si/Si1−xGex. The necessary details of the effective‐mass anisotropy are included in our analysis. We find that it is readily possible to achieve an absorption constant of order of 104 cm−1 in Si quantum wells with current doping technology. For [110] and [111] growth directions, a further advantage of Si quantum wells is pointed out, namely, an allowed absorption at normal incidence due to the anisotropic effective mass in Si.

Analysis of normal‐incident absorption in p‐type quantum‐well infrared photodetectors

Normal‐incident absorption in the recently‐demonstrated, p‐type quantum‐well infrared photodetectors is analyzed with the k⋅p theory, under the envelope‐function approximation. A first‐principles calculation of the infrared‐absorption spectra is performed with no adjustable parameter. The responsivity is evaluated from the calculated normal‐incident absorption and the experimentally‐derived photoconductive gain. Good agreement is obtained with measurements at λ<λc. The bandwidths of the infrared‐absorption spectra are found to be limited by spin‐orbit splitting as well as the overlap integrals.

A proposed collector design of double heterojunction bipolar transistors for power applications

A new collector design for the AlGaAs-GaAs double heterostructure bipolar transistor (DHBT) is proposed, analyzed, and simulated. The base-collector junction is linearly graded and terminated with a highly doped thin layer to offset the adverse alloy grading electric field. Simple analytical formulas are derived to facilitate the implementation of the design. A proof-of-principle simulation has been carried out for an X-band AlGaAs-GaAs power DHBT to confirm the design and the derived formula. The simulation shows the breakdown voltage can be increased from 30 V to about 45 V while the critical current density is about the same. It is also shown that, unlike other refined DHBT structures, the proposed structure does not require critical control in the fabrication of the base-collector junction.<<ETX>>

Theoretical investigations of a proposed series integration of resonant tunneling diodes for millimeter-wave power generation

The double-barrier quantum-well resonant tunneling diode (RTD) has great potential for power generation at millimeter-wave frequencies. If a number of RTDs are integrated in series, the integrated device can greatly increase the total output power and help remove the problem of low-frequency spurious oscillations associated with a single RTD. The feasibility of such a series integration scheme is investigated. The advanced monolithic nonlinear transmission line (NLTL) generating picosecond voltage shock waves can be used to initiate oscillation in such series-integrated RTDs to overcome the DC instability. The large-signal RF characteristics of the series-integrated RTDs are analyzed and simulated, including transit time effects in the depletion region. Available GaAs-AlAs RTD data was used to obtain computer simulation results showing that a total CW output power of about 0.1 W with a DC-to-RF conversion efficiency of about 8% can be generated to a 5- Omega load at 100 GHz, if ten such RTDs are integrated in series. >

Delay of Kirk effect due to collector current spreading in heterojunction bipolar transistors

In this work, we present experimental evidence and develop a simple theory for the delay of base push out (Kirk effect) due to collector current spreading in heterojunction bipolar transistors (HBTs). This effect is very pronounced in small area devices even with short collectors. A correction factor relating the observed emitter current density at which peak cut-off is observed to the classical Kirk effect current limit is derived. This theory has very good agreement with measured data for several different epitaxial structures and has important, implications for the design of both digital and microwave transistors and circuits.

Fundamental and subharmonic excitation for an oscillator with several tunneling diodes in series

Connecting several tunneling diodes in series shows promise as a method for increasing the output power of these devices as millimeter-wave oscillators. However, due to the negative differential resistance (NDR) region in the dc I-V curve of a single tunneling diode, a circuit using several devices connected in series, and biased simultaneously in the NDR region, is dc unstable. Because of this instability, an oscillator with several tunneling diodes in series has a demanding excitation condition. Excitation using an externally applied RF signal is one approach to solving this problem. This is experimentally demonstrated using an RF source, both with frequency close to as well as with frequency considerably lower than the oscillation frequency. Excitation by an RF source with a frequency as low as one-sixth of the oscillation frequency was demonstrated in a proof-of-principle experiment at 2 GHz, for an oscillator with two tunnel diodes connected in series. Strong harmonics of the oscillation signal were generated as a result of the highly nonlinear dc I-V curve of the tunnel diode and a large signal oscillator design. Third harmonic output power comparable to that of the fundamental was observed in one oscillator circuit. If submillimeter wave resonant-tunneling diodes (RTDs) are used instead of tunnel diodes, this harmonic output may be-useful for generating signals at frequencies well into the terahertz range. >

Theory for high Q p-n junction avalanche inductors

A simple theory for p-n junction inductors is presented. The theory explains the previously measured inductances of p-n junction inductors very well. It shows that the measured low quality factors of the earlier report are due to the unnecessary space charge resistances of the p-n junctions adopted in the experiment. A simple theoretical design example of high Q p-n junction inductors is shown to be readily available in silicon.

Inductance probing into the semiconductor breakdown

In this letter, an experimental method to unravel mixed interband tunneling and avalanche effects in heavily doped silicon junctions is presented. This method measures the alternating current impedance in the breakdown regime in addition to the direct current characteristics and clearly extracts the avalanche parameters in the presence of strong tunneling. Many phenomena in the high field transport in silicon were observed due to this capability and have important device applications. The method can be applied to other semiconductors as well.

Analysis and simulation of the quantum well injection transit time diode

The quantum-well injection transit time (QWITT) diode is simulated for two different injection phase angles (90 degrees and 270 degrees ) at 60, 90, 200, and 300 GHz. Quantitative analysis of the output power and efficiency is carried out by including the velocity transient effect, the diffusion effect, and the carrier space-charge effect. The diffusion effect and the carrier space-charge effect degrade the output power and efficiency of the device. The velocity transient effect enhances the device performance for a 270 degrees injection phase mode, but it renders the device useless for a 90 degrees injection phase mode. In comparison with other microwave devices, a simple QWITT diode is a very promising device for millimeter-wave frequency application when it is used with a 270 degrees injection phase angle. This is due to fast intrinsic frequency response time and extremely localized carrier injection mechanism as well as high transient velocity at a small distance. Because of the good efficiency of the QWITT diode, it is feasible to increase output power by integration of many QWITT diodes. >

On the mechanism and frequency limit of double‐barrier quantum‐well structures

Two parameters are adopted to characterize the transport process in double‐barrier quantum‐well (DBQW) structures. It is shown that, in general, both coherent resonant tunneling and incoherent sequential tunneling processes are possible. However, for most high‐frequency applications, large current densities (>104 A/cm2) are required and, therefore, the sequential process is unlikely to occur. To determine the high‐frequency capability, both the adiabatic limit of the dc current‐voltage curve as well as the capacitance charging time in an embedding circuit need to be considered. We confirm that the DBQW structures with barrier thickness of 20 A or smaller can operate up to about 1 THz.