Strumentazione e caratterizzazione dei materiali e dei dispositivi

Strumentazione e caratterizzazione dei materiali e dei dispositivi Mauro Mosca (www. dieet. unipa. it/tfl/) last release: 08/10/2017 Università di Palermo – DEIM

Contents • L-I-V measurements set-up • Misura resistenza di contatto • Catodoluminescenza • Diffrattometro a raggi X

L-I-V measurements set-up source meter semiconductor parameter analyzer of large area (~1 cm 2)

L-I-V measurements set-up: Popt and hext RPD = IPD /Popt

Resistenza di contatto

Resistività di contatto Typical values:

Resistenza di contatto. Geometria laterale

Transmission Line Method (TLM)

Transmission Line Method (TLM)

TLM: current crowding

TLM: transfer length • The transfer length is the average distance that an electron (or hole) travels in the semiconductor beneath the contact before it flows up into the contact. • So the effective area of the contact can be treated as LT W

TLM: transfer length

Transmission Line Method (TLM)

Transmission Line Method (TLM)

Cathodoluminescence (CL) • Cathodoluminescence microscopy is the analysis of luminescence from a material when stimulated by the electron beam of an electron microscope • Cathodoluminescence occurs because the impingement of a high energy electron beam elevates the sample to an excited state, which can then induce it to emit a photon when the sample returns to the ground state • The photon energy (color) and the probability that a photon (not a phonon) will be emitted depends on the material, its purity, and the defects it contains • The emitted signals reveal morphological information, such as size and shape, as well as composition, chemistry, crystallography, electronic properties, plus much more

Cathodoluminescence (CL) ADVANTAGES: • Gives a full description of a sample with direct correlation of a sample’s shape, size, crystallinity or composition with its optical properties • Allows investigation of optical properties at a spatial resolution better than the diffraction limit of light • Allows measurement of dislocation density • Maps defects in integrated circuits. • Well suited to examine low-dimensional semiconductor structures, such a quantum wells or quantum dots.

Cathodoluminescence (CL): electron microscope set-up

Cathodoluminescence (CL): several images CL images Ga. N on sapphire scanning electron microscope and image The CL image shows threading dislocation defects in Ga. N

Cathodoluminescence (CL): several images Zn. O nanobelt scanning electron microscope image and CL images The CL image illustrates defects in the fine structure not observed in the SE image

Diffrazione a raggi X (XRD) (bremsstrahlung) interazione tra fascio di elettroni e target metallico

Diffrazione a raggi X (XRD)

Diffrazione a raggi X (XRD)

Diffrazione a raggi X (XRD): Legge di Bragg

Diffrazione a raggi X (XRD): metodi - Metodo di Laue (q costante, l variabile) - Metodo delle polveri (l costante, q variabile) anche per film policristallini

Diffrazione a raggi X (XRD): diffrattometro (solidale con la fenditura)

Diffrazione a raggi X (XRD): diffrattometro alla Bragg-Brentano

Diffrazione a raggi X (XRD): q-2 q scan

Diffrazione a raggi X (XRD): texture e mosaicità (w-scan) Si fissa l’angolo 2 q e si effettua una scansione in w rocking curve larga in caso di forte Si può così conoscere la ripartizione dei piani angolari disorientazione dei piani cristallini così osservati (bassa texture) grani ad orientazione parallela al frazione volumetrica del cristallo substrato risultano disorientati l’uno orientazione che presentapreferenziale orientazione non-random rispetto all’altro (o texture) FWHM La mosaicità NON è rivelabile con la rocking curve!

Diffrazione a raggi X (XRD): w-scan q-2 q-scan w-scan (rocking curve)

Diffrazione a raggi X (XRD): goniometro a 4 cerchi (f-scan)

Diffrazione a raggi X (XRD): f-scan Figura dei poli

Diffrazione a raggi X (XRD): legge di Scherrer: Deformazioni reticolari legge di Scherrer allargamento dovuto alla dimensione dei grani cristalliti