An important aspect of the large expansion in the development and production of solid-state devices has been the demand for more sophisticated techniques for determining the electrical properties of semiconductors, especially silicon and the III-V compounds. A very wide range of measurement techniques now exists and it is the purpose of this article to review those techniques which are in widespread use or which show promise for future application, and at a time for continuing innovation in this area, to indicate present trends and material problems which may arise in the near future.

https://iopscience.iop.org/article/10.1088/0034-4885/41/2/001/pdf

The electrical characterisation of semiconductors

One of the main problems in measuring the lifetime is how to distinguish the bulk and surface contributions to the total recombination process. The lifetime measured by any method is not only affected by bulk but also by surface recombination processes. Various methods have been suggested, such as immersing the sample in the HF solution, or measuring the fundamental lifetime on wafers which are identical except for the thickness. A microwave lifetime measurement method has been used at a frequency of 2.8 GHz in which the reflected microwave power is proportional to the average excess concentration over the whole thickness of the sample. The advantage of the harmonic generation method and analysis of the amplitude and phase of the reflected microwaves, is that it not only is highly accurate, but also gives the bulk lifetime and the surface recombination velocities at the front and back surfaces separately.

Separate contactless measurement of the bulk lifetime and the surface recombination velocity by the harmonic optical generation of the excess carriers

The influence of the density (Ndis) and of the recombination activity (Sd) of dislocations on the photocurrent (Jsc), the spectral dependence of Jsc and the effective electron diffusion length (Leff) of a P+‐N junction solar cell are computed by means of a model which makes use of the Green’s function method. In this model Sd is the surface recombination velocity of the space‐charge cylinder surrounding the dislocation line and the dislocations are assumed to be perpendicular to the illuminated surface of the cells and homogeneously recombining. The results obtained indicate that the values of Jsc and their spectral variations, as well as values of Leff, are dependent on both Ndis and Sd, especially when Ndis and Sd are larger than 103 cm−2 and 104 cm s−1, respectively. The base thickness (d) of the cells and the value of electron diffusion length (Ln) in the undislocated regions of the wafers are also introduced in the model as independent parameters.

Influence of dislocations on electrical properties of large grained polycrystalline silicon cells. I. Model

Carrier lifetime in silicon and its impact on solar cell characteristics

The lifetime and diffusion constant of minority carriers in Si have been determined by a phase‐shift technique using an electron‐beam‐induced current (EBIC). The phase of an EBIC is shifted because of the recombination of minority carriers in a material when the intensity‐modulated electron beam is used in the line scan method of EBIC. The phase shift between the electron beam and the EBIC is clarified theoretically by solving the three‐dimensional time‐dependent diffusion equation. The phase shift increases linearly with the scanning distance. The relation between the phase shift and lifetime τ was found to be expressed using the approximated solutions of the one‐dimensional diffusion equation with empirical correction factors. The normalized phase shift (i.e., the amount of the phase shift when the beam scans over one diffusion length) becomes a function of only ωτ (ω = 2πf, where f is modulation frequency). With the aid of a curve of the normalized phase shift vs ωτ, the lifetime and diffusion constant can be determined without any restriction for modulation frequency. Experimental results in Si showed good agreement with the theory.

Determination of lifetime and diffusion constant of minority carriers by a phase‐shift technique using an electron‐beam‐induced current

The influence of finite surface recombination velocity on the measurement of minority carrier lifetime has been studied. The method is based on measuring the phase shift between the a.c.-photocurrent of a Schottky contact and the incident light. The limit of spatial resolution has been shown by theoretical calculations to be about one diffusion length. Lifetime profiles have been measured by the use of a mercury capillary contact.

H. Reichl

Papers

Measurement of minority carrier lifetime profiles in silicon