Research at UMass Lowell
Noah P. Allen

Upcoming/Proposed Publications
Modeling Forward and Reverse IVT Schottky Characteristics on GaN with a Log-Normal Barrier Height Distribution

Summary of Expected Publication

The Effect of Annealing Ru Schottky Contacts on IVT Characteristics

Summary of Expected Publication

Impact of Increasing TMGa and Silane on GaN Carrier Concentration and Deep Level Defects by MOCVD

Summary of Expected Publication

GaN PN Diode IVT/CVT Characterization

The temperature dependent characterization of GaN PN Diodes is interesting because the region we typically consider the R-G limited region has a very odd roll-over effect in addition to specific thresholds of reverse leakage current. Using the CVT results, an argument can be made for why each of these regions varies from ideal.

Characterization of Low Doped GaN Temperature Dependence

Low doped GaN can be quite difficult to achieve and I have witnessed samples with moderate doping at RT (300K) and fully depleted at <225K. This paper would describe the phenomenon and explain why it occurs.

Proposed Research Topics
Stress Induced Trapping Perturbation in GaN Films
Target: DOE Basic Energy Sciences (F) (BES)

When gallium nitride is grown in its polar form, inducing stress in the film at the surface can be used for unique applications like the popular HEMT. The research proposed here is a systematic measurement of induced internal polarization fields in GaN films grown on GaN substrates. The idea is to create a model for the inevitable trapping characteristic variation and how it effects the IV properties of fabricated diodes. This work will then play into the 'Non-Contact Estimation of GaN Layers' project.

Characterization and Removal of Interface Charge at Regrown GaN Interfaces

Regrowing GaN interfaces can be interesting on two fronts, allowing businesses to offer a 'Thick GaN Drift Layer' product which clients can then grow and patter on top of to create high power vertical devices or as a method of creating thick GaN drift layers from multiple regrowths. However it has been shown that when this is done, a silicon spike appears and induces a lateral sheet charge which for lateral devices is devastating. Experiments on vertical devices is non-existent thus we propose to understand and remove the incorporation of silicon at regrown interfaces.

Multi-Frequency Impedance Measurement Tools and Techniques

Currently only three companies offer a fast capacitance meter capable of capturing DLTS/DLOS transients. Digitizing and processing a summation of AC perturbation signals presents a unique opportunity to measure all three of the impedance components in a typical non-ideal device. This is important since these components can cause misinterpretation of the data or make it impossible to even measure a device.

Non-Contact Estimation of GaN Layer Capabilities

Although more companies are beginning to offer full GaN substrates for lattice matched growth, they can be grown by different methods and have completely different properties. One of the concerns is that the lattice mis-cut, w.r.t. a flat, can vary across the sample resulting in varying electrical properties across a single sample. Preliminary work has been done by Avogy and SCIOCS to show the free carrier concentration and PL signal intensity variation dependence on mis-cut but work needs to be done to understand the high power device effects. Additionally, work would be done to mitigate the problem during MOCVD growth.