Temperature and doping dependencies of electrical properties in Al-doped 4H-SiC epitaxial layers

Abstract

The free hole concentration and the low-field transport properties of Al-doped 4H-SiC epilayers with several acceptor concentrations grown on semi-insulating substrates have been investigated in the temperature range from 100 to 500 K by Hall-effect measurements. Samples have been grown by cold-wall chemical vapor deposition ͑CVD͒ in the Al acceptor concentration range from 3 ϫ 10 15 to 5.5ϫ 10 19 cm −3 . The dependencies of the acceptor ionization ratio at 300 K and the ionization energy on the acceptor concentration were estimated. Numerical calculations of the hole Hall mobility and the Hall scattering factor have been performed based on the low-field transport model using relaxation-time approximation. At the low acceptor concentrations, the acoustic phonon scattering dominates the hole mobility at 300 K. At the high acceptor concentrations, on the other hand, the neutral impurity scattering dominates the mobility. A Caughey-Thomas mobility model with temperature dependent parameters is used to describe the dependence of the hole mobilities on the acceptor concentration, and the physical meanings of the parameters are discussed.

Analytical formula for temperature dependence of resistivity in p-type 4H-SiC with wide-range doping concentrations

“…−3 ) increased at high temperatures because almost all acceptors are ionized, while the mobility decreases due to enhanced phonon scattering. 20,21,26) On the other hand, the resistivity of the samples with high doping concentrations 300 400 500 600 700 800 900 1000 10 , respectively. The blue, orange, red, and black solid lines are fitting curves obtained from Eqs.…”

“…1, the resistivity of p-type SiC strongly depends on the temperature and doping concentration, which is attributed to the large ionization energy of Al acceptors (∼200 meV) and complicated carrier scattering mechanisms in SiC. 20,21,26) Thus, it is difficult to creat a simple equation or an empirical formula for the fitting. In order to acquire the fitting equation, the dependences of resistivity on the temperature and doping concentration should be considered separately.…”

“…The physical properties of n-type SiC have extensively been investigated so far, [15][16][17][18][19] and those of p-type SiC have also been obtained recently. [20][21][22][23][24][25][26] In our studies, the temperature dependences of hole mobility, hole concentration, and Hall scattering factor were shown by performing Hall-effect measurement on thick p-type SiC epilayers with various doping concentrations. 24,26) Although the resistivity of p-type SiC can be estimated from these data, 24,26) it is much more useful to give an analytical expression that describes the temperature dependence of resistivity.…”

A comparative study on electrical characteristics of 1-kV pnp and npn SiC bipolar junction transistors

“…First, in the case of the emitter doping concentration of 2 × 10 18 cm −3 , the emitter carrier concentration is estimated to be 1.5 × 10 17 cm −3 by assuming the ionization energy as 0.18 eV at room temperature. 25) Therefore, the ratio of the carrier concentration in the emitter to that in the base layer is less than unity and the current gain will be very low. The emitter doping concentration should be increased to improve the injection efficiency.…”

Calibration on wide-ranging aluminum doping concentrations by photoluminescence in high-quality uncompensated p-type 4H-SiC

“…These methods have revealed important electronic properties in both n-and p-type 4H-SiC. [4][5][6][7][8][9][10][11] However, these methods either require formation of contacts or destroy the specimens, which makes them inapplicable in wafer-scale characterization.…”