Page 252 - Photonics Essentials an introduction with experiments

Experimental Photonics: Device Characterization in the Laboratory

246 Characterizing Photonic Devices in the Laboratory

sponding course work. There are six activities covering I–V character-
istics, lock-in detection, the monochromator/spectrometer, light-emit-
ting diodes, capacitance, and lock-in detection. The information in
this chapter is intended as a guideline because the actual details of
the experimental program will depend on the resources that are avail-
able, as well as on the objectives of your instructor.

11.1 Current–Voltage Characteristics of
Photodiodes and LEDs

Objectives
1. Using a curve tracer to study the electrical properties of diodes
2. Understanding the effect of light on current–voltage characteris-
tics
3. Measuring the relationship between the light emitted from an
LED and the bias voltage and current.

Background
The mathematical model of the current–voltage relationship for the
photodiode from Chapter 3 gives a good overall account of the behav-
ior you will encounter in the laboratory. There are some exceptions,
however, and you should aim to identify the experiments in which the
correspondence between the model and the experiment are satisfacto-
ry. You should also identify the cases in which the correspondence is
not so good and suggest how the model could be improved. In the fol-
lowing measurements, you will learn to determine the polarity of the
diode and to measure the photoresponse in both photocurrent modes.

Recommended Equipment
1. Silicon photodiode
2. Germanium photodiode or GaInAs photodiode
3. A device socket
4. Curve tracer

Procedure
a) Build a Mount for the Photodiode. A photodiode is typically packaged
with two pliable metal leads. These are often long enough so that alli-
gator clips can be attached directly to the diode. This procedure, al-
though tempting, usually results in the leads being broken off where
they enter the photodiode package. Thus, the first step consists of

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