Frenkel Emission Research Articles

Emission and capture characteristics of deep hole trap in n-GaN by optical deep level transient spectroscopy

Emission and capture characteristics of a deep hole trap (H1) in n-GaN Schottky barrier diodes (SBDs) have been investigated by optical deep level transient spectroscopy (ODLTS). Activation energy (E emi) and capture cross-section (σ p) of H1 are determined to be 0.75 eV and 4.67 × 10−15 cm2, respectively. Distribution of apparent trap concentration in space charge region is demonstrated. Temperature-enhanced emission process is revealed by decrease of emission time constant. Electric-field-boosted trap emission kinetics are analyzed by the Poole−Frenkel emission (PFE) model. In addition, H1 shows point defect capture properties and temperature-enhanced capture kinetics. Taking both hole capture and emission processes into account during laser beam incidence, H1 features a trap concentration of 2.67 × 1015 cm−3. The method and obtained results may facilitate understanding of minority carrier trap properties in wide bandgap semiconductor material and can be applied for device reliability assessment.

Effect of Hydrostatic Pressure on the Revers Gate-Current of AlGaN/GaN HEMTs

In this paper, we present an Analytical-Numerical model for reverse gate leakage current in AlGaN/GaN high electron mobility transistors (HEMTs), which investigate the influence of the hydrostatic pressure (HP) on gate-current. Salient features of the model are incorporated of occupied sub-bands in the interface quantum well, combined with a self-consistent solution of the Schrödinger and Poisson equations. Finite difference techniques have been used to acquire energy eigenvalues and their corresponding eigenfunctions of AlGaN/GaN (HEMTs). It has been found that the bound charge at the heterointerface has the most impact on the threshold voltage. The increases in hydrostatic pressure cause an increase in threshold voltage. With increasing HP, the Schottky barrier height decreases, AlGaN electric field and reverse gate leakage current are increased. The increase in HP acts as a positive virtual gate. The dependence on the HP of Poole- Frenkel emission (FP) and Fowler-Nordheim (FN) direct tunneling is more than trap-assisted-tunneling (TAT). Increasing the pressure of 2GPa, the intersection point of PF and TAT varies by 1 volt, the reverse gate current increases by an average of 35%, and the threshold voltage increases to 1.15 V in absolute terms.

Charge Transport Mechanism and Trap Origin in Methyl‐Terminated Organosilicate Glass Low‐κ Dielectrics

The charge transport and trap nature responsible for the leakage current through thermally cured methyl‐terminated organosilicate low‐κ dielectric films are studied. It is found that the Frenkel emission does not describe correctly the charge transport in the studied films. The charge transport occurs via the phonon‐assisted electron tunneling between neutral traps as described in the Nasyrov–Gritsenko model. The obtained thermal trap energy value 1.2 eV is close to that for the oxygen divacancy (SiSiSi cluster) in SiO2. The electron energy loss spectra, photoluminescence excitation of 2.7 eV blue band spectra, and data from the simulation within the density functional theory for the model SiCOH low‐κ structure confirm the presence of oxygen vacancy and divacancy in the studied films. The thermal trap energy value estimated as half the Stokes shift of the blue luminescence also gives a value close to 1.2 eV. It proves the correctness of the Nasyrov–Gritsenko model for describing the charge transport mechanism and the conclusion that oxygen divacancies are traps responsible for the leakage current in the studied low‐κ films.

Multiscale modeling of transport in silicon heterojunction solar cells

Silicon based single junction solar cell technology continued to make significant strides in the past year with new world record module efficiencies being reported for the Panasonic heterojunction with thin intrinsic layer (HIT) module (23.8%) and the SunPower rooftop silicon module (24.1%). The HIT cell which is comprised of amorphous silicon (a-Si) and crystalline silicon (c-Si) currently holds the world record efficiency (25.6%) for a silicon based single junction solar cell. Further improvement in this technology requires a rigorous understanding of the underlying physics of the device. The device performance of a-Si and c-Si heterojunction solar cells depends heavily on the nature of transport at the hetero interface and defect assisted transport through the a-Si. Different microscopic processes dominate transport in different regions of the device and take place across widely varying time scales. In this work we present a multiscale model which utilizes different simulation methodologies to study physics in various regions of the device, namely, the Ensemble Monte Carlo (EMC), Kinetic Monte Carlo (KMC), and Drift Diffusion (DD) solvers. The EMC studies the behavior of the photogenerated carriers at the heterointerface; the KMC analyzes transport of the photogenerated carriers through the intrinsic amorphous silicon (i-a-Si) barrier layer; and the DD solver calculates current and other device properties in the low field regions of the cell. These solvers are then self consistently coupled to analyze device performance. Previously, our KMC simulations have shown that hopping is the main mode of transport through the i-a-Si, and the photogenerated carries are collected by defect emission rather that Poole - Frenkel emission or direct tunneling1. In addition, using EMC simulations we have shown that the photogenerated carriers exhibit non Maxwellian behavior at the heterointerface2. This work specifically describes the self-consistent coupling of the DD and EMC solvers. By adding the EMC solver to the multiscale solver we are able to capture the high field behavior of the photogenerated carriers, and its affect on device parameters such as JSC, VOC, FF and efficiency.

Leakage currents in ferroelectric thin films

The main mechanisms of leakage currents in thin lead zirconate titanate (PZT) ferroelectric films prepared by the sol–gel method are discussed. Four specific regions are determined in I–V dependencies. At very weak fields (10–20 kV/cm), the current falls with the voltage increase as a result of depolarization. In the low fields region (about 70–100 kV/cm), the leakage current decreases with the decrease of voltage ramp speed and its components are the ohmic and displacement currents. In the high fields region (≥130 kV/cm), the leakage current increases with the decrease of step voltage ramp in contrast to the previous case. Possible conductivity mechanisms are the Poole– Frenkel emission and hopping conduction. In the transition region between above-mentioned ones (from 80–90 to ∼130 kV/cm), an abrupt unstable increase of current is observed caused by breakdown of reverse bias Schottky barrier. Depolarization currents are studied for sol–gel PZT films prepared at different preparation conditions.

Characterization of aluminum oxide films on p-type silicon substrate prepared by glass assisted CO2 laser technique

Aluminum oxide (Al2O3) films were deposited on p-type Si 〈100〉 substrate using glass assisted CO2 laser technique. Aluminum trichloride AlCl3 and O2 were used as aluminum and oxygen sources respectively and Ar was used as a carrier gas for AlCl3. The films were deposited at different substrate temperatures ranging from 480 to 830 °C. The effect of thermal annealing on low deposited substrate temperature films was carried out in argon environment. Chemical compositions of the films were studied by using Fourier transform infrared (FTIR) spectroscopy. FTIR spectra showed some characteristic bands of aluminum silicate corresponding to bending and stretching bonds of aluminum oxide in the range 650–750 and 750–850 cm−1 respectively. Energy dispersive X-ray showed presence of aluminum in the films. Capacitance–voltage (C–V) measurements were carried out on MOS devices made of these films. Results indicated density of interface traps D it in the range 1012–1013 eV−1 cm−2. The current density–voltage (J–V) curves of devices suggested Poole–Frenkel and Shcottcky emission mechanisms for carrier transport in MOS devices.

Structural and Electrical Investigations of Pulse-Laser-Deposited ( Pb , Sr ) TiO3 Films at Various Oxygen Partial Pressures

Pulsed-laser deposited (PSrT) films on substrate deposited at various oxygen partial pressures , ranging from , were investigated in this work. PSrT films exhibit (100) preferred orientation at lower and then transit to (110) preferred orientation above . The paraelectricity/ferroelectricity transition and dielectric constant of PSrT films are associated with the preferred orientation and oxygen concentration at various . Furthermore, films deposited at higher exhibit higher breakdown field and smaller leakage current density as a consequence of fewer oxygen vacancies. Except for the case of films deposited at , the conduction mechanism is identified as Schottky emission/Poole–Frenkel emission at low/high electric fields.

Comment on “(Ta1−xNbx)2O5 films produced by atomic layer deposition: Temperature dependent dielectric spectroscopy and room-temperature I–V characteristics” [J. Appl. Phys. 90, 4532 (2001)

Experimental results on the I–V characteristics of Ta2O5 and mixed Ta–Nb oxide films at room temperature, reported by Strømme et al. [J. Appl. Phys. 90, 4532 (2001)], are reinterpreted in terms of multiphonon-assisted electron tunneling from traps. Electron-phonon coupling constant and trap depth values are elucidated. Multiphonon-assisted electron tunneling theory eliminates ambiguities in the values of the dielectric constant and other basic parameters deduced from the Poole–Frenkel, Fowler–Nordheim, or Schottky models. Only in the low-field range must the Frenkel emission be taken into account.