Bart Van Zeghbroeck

Electrical characterization of GaN/SiC n-p heterojunction diodes

GaN/SiC heterojunction diodes have been fabricated and characterized. Epitaxial n-type GaN films were grown using metalorganic chemical vapor deposition (MOCVD) and electron cyclotron resonance assisted molecular beam epitaxy (ECR-MBE) on p-type Si-face 6H-SiC wafers. The I–V characteristics have diode ideality factors and saturation currents as low as 1.2 and 10−32 A/cm2, respectively. The built-in potential in the MOCVD- and ECR-MBE-grown n-p heterojunctions was determined from capacitance–voltage measurements at 2.90±0.08 eV and 2.82±0.08 eV, respectively. From the built-in potential the energy band offsets for GaN/SiC heterostructures are determined at ΔEC=0.11±0.10 eV and ΔEV=0.48±0.10 eV.

Temperature-dependent tunneling through thermally grown SiO2 on n-type 4H– and 6H–SiC

The temperature dependence of field emission through thermally grown silicon dioxide (SiO2) on n-type 4H and 6H silicon carbide (SiC) substrates is reported. Room-temperature SiO2/SiC barrier heights, ΦB, of 1.92 and 2.12 V are extracted for the 4H– and 6H–SiC samples, respectively, using a Fowler–Nordheim analysis. Barrier heights of 2.2 and 2.4 V along with a linear temperature-dependent barrier height lowering, ΔΦB/ΔT, of 2.4 and 2.0 mV/K for 4H– and 6H–SiC are extracted using an alternative analytical expression for tunneling from semiconducting substrates derived previously. In both analyses, the temperature-dependent flatband voltage, using the measured room-temperature value, was included.

ON FIELD EMISSION FROM A SEMICONDUCTING SUBSTRATE

A theoretical examination of field emission from the conduction band of a semiconducting substrate is reported. The analysis includes a comparison with Fowler–Nordheim theory, and it is concluded that the formalism of the Fowler–Nordheim theory is incorrect when applied to carriers originating from a semiconducting substrate. The use of a Fowler–Nordheim analysis results in an error in the extraction of the barrier height that is dependent upon the applied electric field across the oxide, conduction band offset, and temperature. A lower limit of the error was calculated to be between 5% and 15%. An analytical expression is developed to describe the field emission of electrons from the conduction band of a semiconductor.

Fowler–Nordheim tunneling of holes through thermally grown SiO2 on p+ 6H–SiC

Fowler–Nordheim tunneling of holes through thermally grown silicon dioxide on 6H–silicon carbide is reported. Oxides of 5.2, 10, and 14.2 nm thickness were grown on the p+ face of a p+n SiC junction. The p+n junction served to separate the electron and hole tunneling currents. Hole tunneling was found to be the dominant current mechanism through the oxide. Fowler–Nordheim analysis, using a parabolic E–K relationship, was performed to extract a barrier height–effective mass product, ΦB3/2(mox/m0)1/2, for electrons and holes of 2.88%±4.9% and 2.38%±3.8% (V3/2) respectively. An estimate for the effective mass of holes within the oxide was made using both the parabolic and Franz dispersion relations.

Threshold reduction through photon recycling in semiconductor lasers

The threshold pump power of an AlGaAs‐GaAs ridge quantum well laser diode has been reduced by 42% by recycling the spontaneous emission. An integrated photodiode absorbs the spontaneous radiation emitted by the laser diode and converts it back into electrical power. The recycling of this power results in a reduction of the electrical power required to reach the lasing threshold.

High-speed nanoscale metal-semiconductor-metal photodetectors with terahertz bandwidth

A model for the maximum bandwidth achievable in metal-semiconductor-metal photodetectors is developed and simulated to determine the dimensions required for terahertz bandwidth. The bandwidth is found to exceed 1THz for devices with line pitch less than 100nm.

6H and 4H-SiC Avalanche Photodiodes

We report on the fabrication and testing of SiC p-i-n avalanche photodiodes. APDs of 0.25 mm2 area on a-plane (1120) 6H-SiC as well as off-axis Si face 6H and 4H-SiC were successfully fabricated. A beveled mesa was used as edge termination. Recessed windows were formed using reactive ion etching to enhance low-wavelength UV performance. We performed current-voltage tests with and without UV illumination to determine dark current, photocurrent, and gain on selected devices. Dark current was less than 1 pA at 0.5Vbr on multiple devices. Quantum efficiency of 40% or greater was observed for all orientations and polytypes.

Low temperature behaviour of short channel GaAs MESFETs

Abstract Low temperature operation of GaAs MESFETs is of interest for special applications which impose a low ambient temperature on the semiconductor devices and as a way to improve performance because of higher electron mobility, lower leakage currents and reduced thermal noise. This paper focuses on the low temperature d.c. characteristics of short channel GaAs MESFETs with very shallow and highly doped channels. The physics of the device is discussed and the theoretical analysis illustrated with experimental results obtained on devices with gate lengths 1 2 μm over the temperature range 4.2–300 K

High-Contrast Visualization of Anti-Phase Domains and Screw Dislocations in 3C-SiC

Silicon carbide (SiC) is an important wide bandgap semiconductor with many polytypes. 3C-SiC is the only cubic polytype, to be distinguished from the hexagonal polytypes such as 4H-SiC and 6H-SiC. Crystalline 3C-SiC, grown by heteroepitaxy, often contains twin structures, also called anti-phase domains (APDs), that are separated by double positioning boundaries (DPBs). This naturally occurs when growing 3C-SiC, since there are two possible and equally-likely stacking sequences with a relative in-plane rotation of 180 degrees as shown in Figure 1. The challenge faced when imaging these APDs, is that neither optical or scanning electron microscopy provides a clear contrast between the rotated domains, as they are composed of the same material with identical properties. This paper demonstrates high-contrast imaging of such APDs, enabled by channeling of electrons or ions.

6.4: Fabrication of 4H-SiC cold field emitter arrays

A new fabrication method of SiC field emitter arrays has been developed. The new method involves the formation of three-dimensional silicon dioxide masks, dry etching, and tip sharpening. The field emitter arrays were successfully fabricated on 4H-SiC substrates with tip diameter less than 10 nm.