Kenneth E. Kambour

A collective impact ionization theory of lock-on [in pulsed power switches]

Photoconductive semiconductor switches (PCSSs), such as optically-triggered GaAs switches, have been developed for a variety of pulsed power applications. Such switches exhibit unique properties associated with lock-on, a phenomenon associated with bistable switching. In this paper, lock-on is explained in terms of collective impact ionization.

Simulation of Current Filaments in Photoconductive Semiconductor Switches

Photoconductive semiconductor switches (PCSSs), such as optically-triggered GaAs switches, have been developed for a variety of applications. Such switches exhibit unique properties as a consequence of lock-on, a phenomenon associated with the bistable switching of these devices. In this paper, lock-on is explained in terms of collective impact ionization. Furthermore, the effect of defects on the performance of these devices is investigated.

Insight into the multicomponent nature of negative bias temperature instability

A novel measurement technique is used to extract two physically distinct “permanent” (long lived on our experimental time scale, ≤12 000 s) and one recoverable charge components of the negative bias temperature instability in p-channel metal–oxide–semiconductor field effect transistors under inversion and n-channel devices under accumulation. The results suggest that the permanent components are present in both cases, while there is little, if any, recoverable charge present in the case of the n-channel device. A physical explanation is provided involving the band energy diagram to explain these observations.

A Physics-Based Device Model of Transient Neutron Damage in Bipolar Junction Transistors

For the purpose of simulating the effects of neutron radiation damage on bipolar circuit performance, a bipolar junction transistor (BJT) compact model incorporating displacement damage effects and rapid annealing has been developed. A physics-based approach is used to model displacement damage effects, and this modeling approach is implemented as an augmentation to the Gummel-Poon BJT model. The model is presented and implemented in the Xyce circuit simulator, and is shown to agree well with experiments and TCAD simulation, and is shown to be superior to a previous compact modeling approach.

Continuum models for electrical breakdown in photoconductive semiconductor switches

In this paper, continuum models for electrical breakdown are described. These models are based on calculations of the carrier distribution function as a function of electric field and carrier density. In these continuum models, the impact ionization rate is approximated in the extremes of low and high carrier density. These continuum models are used for calculations of electrical breakdown in GaAs. In particular, these models are applied to the operation of photoconductive semiconductor switch (PCSS) devices. This comparison with data suggests that a new physics mechanism is required to explain the PCSS data, a new mechanism is hypothesized.

Negative bias temperature instability threshold voltage shift turnaround in SiGe channel MOSFETs

Negative bias temperature instability (NBTI) has been measured at various temperatures in high-k gate insulator MOSFETs with buried Si0.65Ge0.35 channels and with regular Si surface channels. Previous studies on both surface channel Si devices and Si1−xGex buried channel devices provide evidence for net positive charge trapping as a function of electrical stressing time albeit reduced for the case of Si1−xGex compared to the Si case. In our case, for buried Si0.65Ge0.35, the authors find initial negative charge trapping followed by positive charge trapping at longer times, typically >10−1 s. The effect is accentuated at higher temperatures and yields a turnaround in the measured threshold voltage shift as a function of stress time. Closer examination of NBTI in high-k gate, Si surface devices stressed at room temperature and 90 °C suggests both electron and hole trapping may be present there although the majority effect is hole trapping.

A theory of low‐field, high‐carrier‐density breakdown in semiconductors

Collective impact ionization has been used to explain lock‐on, an optically‐triggered electrical breakdown occurring in some photoconductive semiconductor switches (PCSS’s). Lock‐on is observed in GaAs and InP but not in Si or GaP. Here, a rate equation implementation of collective impact ionization is discussed, and it leads to new insights both about intrinsic electrical breakdown in insulating materials in general and about lock‐on specifically. In this approach, lock‐on and electrical breakdown are steady state processes controlled by competition between carrier generation and recombination. This leads to theoretical definitions for both the lock‐on field and the breakdown field. Our results show that lock‐on is a carrier‐density dependent form of electrical breakdown which exists in principle in all semiconductors. Results for GaAs, InP, Si, and GaP are discussed.

Effect of radiation induced charging on gate-all-around NMOS devices

The need for more reliable and radiation hard complementary metal–oxide–semiconductor compatible devices coupled with an ever increasing shrinkage of device dimensions has led naturally to interest in metal-oxide semiconductor field-effect transistors having nontraditional geometries. One such geometry is the gate-all-around transistor, which has been suggested to be less sensitive than its planar counterpart to the effect of charge build-up at the semiconductor–insulator interface such as that induced by irradiation. In order to explore the radiation hardness of such a structure, the effect of radiation on gate-all-around n-type metal–oxide–semiconductor devices was investigated by computing the effect of charging on the threshold voltage of the device. The radiation sensitivity in ideal structures is explored, and the greater radiation sensitivity found experimentally in some devices is explained.

Direct evidence for interface state annealing in the negative bias temperature instability response

Using a rapid data acquisition methodology, the authors examine the time dependent recovery of the “permanent” component of charge build-up due to the negative bias temperature instability in Si based p-channel field effect transistors in inversion and n-channel devices in accumulation. The authors find clear evidence for recovery of the charge associated with interface states for elevated temperatures (≥150 °C) and for extended times (trecover ∼ 20 000 s). Recovery appears to begin at shorter times for p-channel devices than for n-channel. An explanation is advanced both for the mechanism of interface state annealing and for the difference observed between p and n channel devices.

Avalanche Injection and Lock-On in Photoconductive Semiconductor Switches

Optically-triggered, high-power photoconductive semiconductor switches (PCSSs) composed of semi-insulating GaAs carry current in high carrier-density filaments after the optical trigger is discontinued. This highly conductive mode of operation is called lock-on. The properties of these filaments can be explained by collective impact ionization theory in which energy redistribution by carrier-carrier scattering within the filament enhances the impact ionization rate. This allows these filaments to be sustained by fields which are relatively low compared to the bulk breakdown fields. For GaAs, the sustaining lock-on field is approximately 4.5 kV/cm. For this talk, a hydrodynamic implementation of the collective impact ionization theory is used to compute the temporal evolution of these filaments following optical triggering. These continuum calculations are based on previous calculations in which the steady-state properties of filaments are computed using a Monte Carlo method to solve the Boltzmann equation. The same method will be used to calculated avalanche injection effects in a GaAs avalanche photodiode. The two modes of operation, lock-on and avalanche, will be compared and contrasted. In addition, the effects of carrier recombination at defects will also be discussed.