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Investigation of pre-structured GaAs surfaces for subsequent site-selective InAs quantum dot growth.

Helfrich M, Gröger R, Förste A, Litvinov D, Gerthsen D, Schimmel T, Schaadt DM - Nanoscale Res Lett (2011)

Bottom Line: Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning of the samples prior to regrowth.Successive cleaning steps were analyzed and optimized.A UV-ozone cleaning is performed at the end of sample preparation in order to get rid of remaining organic contamination.

View Article: PubMed Central - HTML - PubMed

Affiliation: DFG-Center for Functional Nanostructures (CFN) and Institut für Angewandte Physik, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany. daniel.schaadt@kit.edu.

ABSTRACT
In this study, we investigated pre-structured (100) GaAs sample surfaces with respect to subsequent site-selective quantum dot growth. Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning of the samples prior to regrowth. Successive cleaning steps were analyzed and optimized. A UV-ozone cleaning is performed at the end of sample preparation in order to get rid of remaining organic contamination.

No MeSH data available.


Related in: MedlinePlus

AFM images of samples at different stages of the cleaning procedure: after cleaning with solvents (a), using a heated ultrasonic bath (b), and after UV-ozone cleaning (c).
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Figure 5: AFM images of samples at different stages of the cleaning procedure: after cleaning with solvents (a), using a heated ultrasonic bath (b), and after UV-ozone cleaning (c).

Mentions: Cleaning samples after EBL comprises several steps. First, the resist needs to be removed which is done with an adequate remover. Thereafter, the sample is cleaned with different solvents (trichlorethylene, acetone, isopropyl alcohol, methanol), if possible in a heated ultrasonic bath. Finally, the samples are rinsed in bi-distilled water. The resist used for EBL contains organic compounds. Especially the high temperature during dry-baking of the resist results in a high stability of such compounds against solvents. Critical steps of the cleaning procedure are depicted in Figure 5. The sample in Figure 5a was cleaned using steps one and two of the above procedure but without ultrasonic bath. A lot of contamination is observed from the AFM image (large particles appearing white). When the samples are cleaned in a heated ultrasonic bath, the amount of contamination is reduced. Especially the amount of smaller particles has decreased, as seen in Figure 5b. However, there are still larger areas of residues remaining on the surface. In order to get rid of these remaining contaminants a UV-ozone cleaning step is introduced. It utilizes a low-pressure mercury lamp that emits radiation at the relevant wavelengths of 184.9 and 253.7 nm [9]. Molecular oxygen is dissociated by the shorter wavelength with the atomic oxygen subsequently forming ozone. Ozone is then decomposed by the longer wavelength. Atomic oxygen is thus constantly provided. In addition, the 253.7 nm radiation excites organic molecules. These react with the atomic oxygen and form simpler, volatile compounds that desorb from the surface. The effect of UV-ozone cleaning is displayed in Figure 5c where essentially all contamination has disappeared. As a result, the number of defect holes should be drastically reduced resulting in a uniform and flat GaAs BL after regrowth. Clean oxygen was fed throughout the cleaning process. UV-ozone cleaning is a very gentle process which does not bombard the surface with ions. The cleaning efficiency is comparable to conventional plasma ashing. However, the costs for appropriate UV-ozone cleaners are much lower. In fact, such devices can easily be self-built.


Investigation of pre-structured GaAs surfaces for subsequent site-selective InAs quantum dot growth.

Helfrich M, Gröger R, Förste A, Litvinov D, Gerthsen D, Schimmel T, Schaadt DM - Nanoscale Res Lett (2011)

AFM images of samples at different stages of the cleaning procedure: after cleaning with solvents (a), using a heated ultrasonic bath (b), and after UV-ozone cleaning (c).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211268&req=5

Figure 5: AFM images of samples at different stages of the cleaning procedure: after cleaning with solvents (a), using a heated ultrasonic bath (b), and after UV-ozone cleaning (c).
Mentions: Cleaning samples after EBL comprises several steps. First, the resist needs to be removed which is done with an adequate remover. Thereafter, the sample is cleaned with different solvents (trichlorethylene, acetone, isopropyl alcohol, methanol), if possible in a heated ultrasonic bath. Finally, the samples are rinsed in bi-distilled water. The resist used for EBL contains organic compounds. Especially the high temperature during dry-baking of the resist results in a high stability of such compounds against solvents. Critical steps of the cleaning procedure are depicted in Figure 5. The sample in Figure 5a was cleaned using steps one and two of the above procedure but without ultrasonic bath. A lot of contamination is observed from the AFM image (large particles appearing white). When the samples are cleaned in a heated ultrasonic bath, the amount of contamination is reduced. Especially the amount of smaller particles has decreased, as seen in Figure 5b. However, there are still larger areas of residues remaining on the surface. In order to get rid of these remaining contaminants a UV-ozone cleaning step is introduced. It utilizes a low-pressure mercury lamp that emits radiation at the relevant wavelengths of 184.9 and 253.7 nm [9]. Molecular oxygen is dissociated by the shorter wavelength with the atomic oxygen subsequently forming ozone. Ozone is then decomposed by the longer wavelength. Atomic oxygen is thus constantly provided. In addition, the 253.7 nm radiation excites organic molecules. These react with the atomic oxygen and form simpler, volatile compounds that desorb from the surface. The effect of UV-ozone cleaning is displayed in Figure 5c where essentially all contamination has disappeared. As a result, the number of defect holes should be drastically reduced resulting in a uniform and flat GaAs BL after regrowth. Clean oxygen was fed throughout the cleaning process. UV-ozone cleaning is a very gentle process which does not bombard the surface with ions. The cleaning efficiency is comparable to conventional plasma ashing. However, the costs for appropriate UV-ozone cleaners are much lower. In fact, such devices can easily be self-built.

Bottom Line: Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning of the samples prior to regrowth.Successive cleaning steps were analyzed and optimized.A UV-ozone cleaning is performed at the end of sample preparation in order to get rid of remaining organic contamination.

View Article: PubMed Central - HTML - PubMed

Affiliation: DFG-Center for Functional Nanostructures (CFN) and Institut für Angewandte Physik, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany. daniel.schaadt@kit.edu.

ABSTRACT
In this study, we investigated pre-structured (100) GaAs sample surfaces with respect to subsequent site-selective quantum dot growth. Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning of the samples prior to regrowth. Successive cleaning steps were analyzed and optimized. A UV-ozone cleaning is performed at the end of sample preparation in order to get rid of remaining organic contamination.

No MeSH data available.


Related in: MedlinePlus