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Author:Segercrantz, Natalie
Title:Inverkan av kväve, vismut och temperatur på vakans- och defektdistributionen i GaSb
Influence of nitrogen, bismuth and temperature on the vacancy and defect distribution in GaSb
Publication type:Master's thesis
Publication year:2013
Pages:67      Language:   swe
Department/School:Perustieteiden korkeakoulu
Main subject:Ydin- ja energiatekniikka   (Tfy-56)
Supervisor:Tuomisto, Filip
Instructor:Slotte, Jonatan
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201307037156
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  3   | Archive
Keywords:Doppler spectroscopy
positron annihilation spectroscopy
coincidence
defect
vacancy
GaNSb
GaSbBi
GaSb
Dopplerspektroskopi
positronannihilationsspektroskopi
koincidens
defekt
vakans
Abstract (eng): In this master's thesis, defect studies in GaNSb and GaSbBi epitaxial layers and bulk GaSb using positron annihilation spectroscopy (PAS) in Doppler broadening mode were performed.
PAS is a non-destructive spectroscopic technique for studying vacancies and open volume defects.
The technique is based on the interaction between positrons and the electrons of a material.
By measuring the Doppler broadening of the annihilation line, information on the size, concentration and charge of the defect can be obtained.

Coincidence Doppler was also used for studying the samples.
For coincidence Doppler, two detectors are used which reduces the background so that the Doppler broadening at higher momenta can be profiled.
Thus, identification of the chemical surrounding of the defect is possible.

From the results for the samples with GaNSb and GaSbBi epitaxial layers, a relationship between the concentration of N/Bi in the epitaxial layer and the vacancy concentration seems to exist.
This was seen as a decrease in the S-parameter and an increase in intensity at a momentum of 1.2 a.u. compared to the n-type bulk.

Undoped, unintentionally p-type and doped n-type GaSb bulk samples were measured at both high and low temperatures.
Since the position of the Fermi level in the band gap, the formation enthalpy of defects and their ability to trap positrons are temperature dependent, measurements at different temperatures give additional information on the type and charge of the defect.

The results from measurements at different temperatures with bulk GaSb show a relationship between the S-parameter and the temperature.
Increased positron trapping into negative ions competing with reduced concentrations of negative or neutral vacancies was proposed as a possible explanation for the low S-parameters at low temperatures.
When the temperature is increased, the S-parameter increases and the ability of the vacancies to trap positrons seem to change.

In addition, hysteresis in the results for both bulk samples can be seen.
For the p-type sample the effect could be seen at low temperatures, whereas for the n-type sample hysteresis appeared at high temperatures.
Metastable defects could be the reason for the hysteresis, which according to calculations could exist in GaSb.
Abstract (swe): I detta diplomarbete användes positronannihilationsspektroskopi (PAS) för defektstudier i GaNSb och GaSbBi epitaxiallager samt odopat och dopat bulk GaSb.
PAS är en icke-destruktivt spektroskopisk metod för defektstudier i fasta material.
Metoden baserar sig på positroners växelverkan med materialets elektroner och lämpar sig speciellt väl för att studera vakanser samt defekter med öppna volymer.
Genom att mäta Dopplerbreddningen för annihilationslinjen kan information om defektens storlek, laddning och koncentration erhållas.

Även koincidensdoppler tillämpades för att undersöka proverna.
Vid koincidensdoppler används två detektorer vilket reducerar bakgrunden och möjliggör profilering av Dopplerbreddningen vid högre rörelsemängder.
Vakansers kemiska omgivning kan såldes undersökas och identifieras.

Resultaten för proverna bestående av GaNSb och GaSbBi epitaxiallager uppvisade ett förhållandet mellan andelen N/Bi i epitaxiallagret och vakanskoncentrationen.
Detta syntes som lägre värden på S-parametern samt som en intensitetsökning vid en rörelsemängd motsvarande 1,2 a.u. jämfört med n-typs bulken.

Proverna bestående av odopat, oavsiktligt p-typs och dopad n-typs GaSb mättes vid både höga och låga temperaturer.
Eftersom ferminivåns höjd, formationsentalpin för defekter samt deras förmåga att fånga positroner beror på temperaturen ger mätningar vid olika temperaturer ytterligare information om defekters typ och laddning i provet.

Mätningar med bulk GaSb vid olika temperaturer visade ett förhållande mellan S-parametern och temperaturen.
De låga värdena på S-parametern vid låga temperaturer tros bero på att negativa joner fångar positroner mera effektivt medan koncentrationen av negativa eller neutrala vakanser sjunker.
Då temperaturen höjs och S-parametern ökar verkar vakansers förmåga att fånga positroner förändras.

En hysteresiseffekt kunde desutom ses i resultaten för både p- och n-typs GaSb.
För p-typs provet observerades detta vid låga temperaturer, medan för n-typs provet mättes effekten endast vid höga temperaturer.
Hysteresen kunde bero på metastabila defekter som enligt beräkningar kunde existera i GaSb
ED:2013-06-17
INSSI record number: 46896
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