High-Resolution
Low-Temperature PLof Semiconductors

OSD-110

Characterize defects andimpurities in semiconductors
Introduction
Temperature-dependent photoluminescence (PL)spectroscopy is a powerful optical method forcharacterizing materials. PL can be used to identify
defects and impurities in Si and III-V semiconductors,
as well as determine semiconductor bandgaps. At room
temperature, PL emission is usually broad—up to 100 nm
in width. When samples are cooled, structural details may
be resolved; a small spectral shift between two samples
may represent a difference in structure. For cooling, twotypes of cryostat typically are used: a cryostat using
liquid N2 or liquid He, or a closed-cycle cryostat in whichcryogenic liquid is included as part of the cooling system.
The cooled sample is excited by a laser, and the PL iscoupled to a spectrometer via an optical interface. In thisTechnical Note, sample data are shown from a highresolution PL system.
Experimental setup
A 1 m focal-length monochromator (1000M Series
II, 600 gr/mm grating) scanned from 800–1650 nm.
The detection system was a thermoelectrically cooled
InGaAs detector with chopper and lock-in amplifier.
Semiconductor samples were mounted in a closedcycle cryostat mounted above the optical table, andcooled to 4.5 K. A HORIBA Scientific Low Temperature
Cryostat Interface optimized the optical coupling into themonochromator. The excitation source was a 10 mW
HeNe laser (λ= 632.8 nm). Fig. 1 shows the experimental
apparatus.
Results
Fig. 2 shows spectra of the same sample measured atroom temperature and at 4.5 K. In PL spectroscopy,a material absorbs light, creating an electron-holepair. An electron from the valence band jumps to theconduction band, leaving a hole in the valence band. The
photon emitted upon recombination corresponds to theFigure 1. Experimental system.

energy-difference between the valence and conduction
bands (bandgap), and is hence lower in energy than theexcitation photon, so that the emission is red-shifted withrespect to the excitation light. At low temperatures, a PL
peak is quite sharp. As the temperature increases, thepeak broadens and shifts to lower
energy. This red-shift, typical forsuch materials, indicates bandgap

shrinkage as a function of temperature. The decrease inpeak intensity indicates that electrons escape via nonradiative processes.
Fig. 3 compares PL spectra from a sample of Nd:YAG
laser-glass, using the 1000M Series II (1 m focal length)
and the iHR320 (0.32 m focal length) spectrometers.
Note the sharper peaks recorded with the 1000M system.

HORIBA Scientific component

Part number

Low Temperature PL Optical Interface

ACC-CRYO-1000M

1000M Series II, 2 entrance and 1 exit slits

1000M II

Optical Chopper

ACH-C

Lock-in Amplifier

SR810Solid-state detector interface

1427C

Thermoelectrically cooled InGaAs
photodiodeDSS-IGA020T

SynerJY® spectroscopy software

CSW-SYNERJY

Closed-cycle He cryostat

Contact us

Cryostat-mounting hardware

Contact us

Figure 2. PL from typical semiconductor sample at room temperature, and alsocooled to 4.5 K.

Figure 3. PL spectra of Nd:YAG laser-glass, taken with (black) iHR320 spectrometerand (red) 1000M spectrometer.

info.sci@horiba.com
USA: +1 732 494 8660
UK: +44 (0)20 8204 8142
China: +86 (0)21 6289 6060

www.horiba.com/scientificFrance: +33 (0)1 69 74 72 00
Italy: +39 2 5760 3050
Brazil: +55 (0)11 5545 1500

Germany: +49 (0)89 4623 17-0
Japan:+81 (0)3 6206 4721
Other:+33 (0)1 69 74 72 00

This document is not contractually binding under any circumstances - Printed in USA - ©HORIBA Scientific 07/2014

System components
In order to measure photoluminescence ofsemiconductors, the following are needed: a stable,
powerful monochromatic light source, optics to focus
light on the sample, a sample holder, collection optics, aspectrometer, and a detector for spectral analysis. TheLow Temperature PL Optical Interface from HORIBA
Scientific provides a stable collection-optics system, tocollect the maximum amount of light from the sample
inside either type of cryostat, and couple it efficiently into
the spectrometer. Benefits include:• Reflective optics for maximum light collection• Compatible with M-Series, iHR320/550, andFHR640/1000 spectrometers• Mounts directly on the spectrometer entrance slit
• Compatible with most cryostats with 90 mm dia.
bodies• Input f/1.5, output f/7.5• Filter-holder included [standard 1″ (2.5 cm) filter]