4 research outputs found
Van der Waals and Graphene-Like Layers of Silicon Nitride and Aluminum Nitride
A systematic study of kinetics and thermodynamics of Si (111) surface nitridation under ammonia exposure is presented. The appeared silicon nitride (8 × 8) structure is found to be a metastable phase. Experimental evidences of graphene-like nature of the silicon nitride (8 × 8) structure are presented. Interlayer spacings in the (SiN)2(AlN)4 structure on the Si (111) surface are found equal to 3.3 Å in SiN and 2.86 Å in AlN. These interlayer spacings correspond to weak van der Waals interaction between layers. In contrast to the widely accepted model of a surface structure (8 × 8) as monolayer of β-Si3N4 on Si (111) surface, we propose a new graphene-like Si3N4 (g-Si3N3 and/or g-Si3N4) model for the (8 × 8) structure. It is revealed that the deposition of Al atoms on top of a highly ordered (8 × 8) structure results in graphene-like AlN (g-AlN) layers formation. The g-AlN lattice constant of 3.08 Å is found in a good agreement with the ab initio calculations. A transformation of the g-AlN to the bulk-like wurtzite AlN is analyzed
Negative Differential Resistance Observation and a New Fitting Model for Electron Drift Velocity in GaN-Based Heterostructures
The aim of this paper is an investigation of electric field-dependent
drift velocity characteristics for Al0.3Ga0.7N/AlN/GaN heterostructures
without and with in situ Si3N4 passivation. The nanosecond-pulsed
currentvoltage (I-V) measurements were performed using a 20-ns applied
pulse. Electron drift velocity depending on the electric field was
obtained from the I -V measurements. Thesemeasurements showthat a
reduction in peak electron velocity from 2.01 x 10(7) to 1.39 x 10(7)
cm/s after in situ Si3N4 passivation. Also, negative differential
resistance regime was observed which begins at lower fields with the
implementation of in situ Si3N4 passivation. In our samples, the
electric field dependence of drift velocitywas measured over 400 kV/cm
due to smaller sample lengths. Then, a wellknown fitting model was
fitted to our experimental results. This fitting model was improved in
order to provide an adequate description of the field dependence of
drift velocity. It gives reasonable agreement with the experimental
drift velocity data up to 475 kV/cm of the electric field and could be
used in the device simulators