High injection effects on conductivity and carrier lifetime in P-type silicon material

Abstract

High injection changes in carrier lifetime, mobility and density of a semiconductor material are analyzed using the changes in carrier recombination or diffusion processes and in equilibrium of the donor-acceptor centers (including defect centers). The analysis especially involves the variations with carrier injection Δ of state charge q0 and energy level E occupancy state nE(pE) of the material recombination or donor (acceptor) centers, taking into account the Δ, band-gap energy level E, material Fermi-level EF and center capture cross section σ cn,p values. The above variations and high injection changes are then discussed in terms of their effects on the magnitude, rise and decay of the material transient photoresponses of conductivity Δ V(t) and minority carrier diffusion current iD(t). High injection effects on the conditions under which these photoresponses are observed are also pointed out in this paper. With the view of illustrating the above analysis, experimental results are shown which deal with ~ 1 and 10 Ω.cm P-type silicon samples, submitted to Δ ~ 10-3 to 103 × p0 carrier injection by neodymium laser pulses of 55 ns duration. Low dose irradiation by 14 MeV neutrons (9.6 x 1011 n.cm-2) is used to demonstrate the role of material defects in high injection phenomena. Using the comparison between the photoconductivity and minority carrier diffusion current measured responses, the results especially show that acceptor centers are created by the irradiation (E A = Ev + 0.09 eV, σcp = 10-17 cm-2) whose effect is to lower the effects due to the previously existing donor centers (ED ∼ Ec - 0.08 eV, σcn ~ 1.5 × 10-18, in the un-irradiated samples)

Plan View and Cross-Sectional View EBIC Measurements: Effect of e-Beam Injection Conditions on Extracted Minority Carrier Transport Properties

“…The diffusion length reaches a maximum value at the injection level within an order of magnitude of the base doping. It was shown that the minority carrier lifetime and diffusion length could be increased at high injection level, because of enhanced density of ionized centers [12], [24]. It should be mentioned that the diffusion length range for extreme boundary conditions (n=0, 1/2) significantly increases for high-level injection conditions.…”

Charge carrier properties in P-type layers of silicon on sapphire

“…-The general forms of the photoresponses i(t) and 0394V03C3(t) are the same at 1.06 03BCm and 0.53 gm. These two types of photoresponses, which correspond respectively to free electrons or holes (photocurrent in,p(t)) and to the variation in the conductivity induced in the material, may be related to diverse phenomena (see [4]). They are compared in figure 7.…”

“…The values of 03C403C31 and 'ta2 are given in figure 7 ; note that they are large. This is therefore not the response of a homogeneous material such as bulk silicon, in which the lifetime of free carriers may be measured from the photoconductivity decay, at least in the low to mean carrier injection range [4,13,14].…”

“…For the case of 1.06 pm light pulses where G is estimated from the intensity Eo (mJ) incident on the sample for a surface reflection of 20 % and an absorption coefficient a = 40 cm -1, we obtain : Since the incident energy used Eo (1.06 pn) varied between -10-4 mJ and I02/mJ, the measurements done at ambient temperature with 1.06 03BCm light correspond to the followin$ range of excess electron or hole densities,' where oiv to high injection rates An, plpo thus appear involved : epitaxial layer w = 0.9 gm epitaxial layer w = 1.3 ym epitaxial layer w = 2.4 g 4.2 ANALYTICAL DESCRIPTION OF TRANSIENT PHOTO-RESPONSE RESULTS. -We recall first that, for the three cases of transient photoresponses that are used in the present work, the responses given by the epitaxial samples must be considered a priori as the sum of two contributions : a primary contribution which agree with a contribution of excess free carriers, and a secondary contribution which appears as a perturbation of the electrical state of the material following the injection of these free carriers, e.g., perturbation of the electronic occupation state nE, pE of energy levels E located in the bandgap, and therefore of the charge carrier density, p( po, Ap, Y nl), y pA), mobility, Jl(Po + An, p), in the material, etc... [4]. where ao is the equilibrium conductivity of the mate-, rial (P-type).…”

“…to the photoconduction processes. It uses the results of previous research on bulk silicon [4] and polycrystalline silicon [5,6].…”