In-Containing Compound Semiconductors - Sample Preparation for TEM

Application Note for Leica EM RES102 - Industrial Manufacturing

December 12, 2016

Previous studies showed that surface accumulation of In occurs when InP was milled in a conventional way with Ar ions. The consequence is In islands on the sample surface. This leads to low quality of TEM samples. To remove these islands, reactive ion milling with iodine ions (RIBE / CAIBE) can be used. This method has the disadvantage of polluting the ion guns and the vacuum system of the ion milling device and leads to chemical reactions with the sample material. To avoid these problems we prepared these samples very gently with low energy Ar ions.

Preparation Conditions
Mechanical pre-preparation:
Preparation of InGaAsP / InP MQW (Multiple Quantum Well)- structures and InP-samples. The samples were double-sided dimpled. A milling angle lower than 7° was not possible.

Ion milling:

Sample holder:Quick-clamp-holder
Acceleration voltage:4 kV and 2 kV (final step)
Milling angle:7° (double-sided milling)
Sample movement:Rotation and Oscillation (alternating)

 

Results
The use of small milling angles and low ion energy results in very clean samples. No In islands are visible on the samples. The lattice image of [110] oriented InP shows a nearly perfect lattice. This proves, that by using the correct milling parameters, conventional ion milling can also achieve very good preparation results. We could avoid reactive ion milling with iodine ions.

Fig.1: Cross-sectional TEM images of a conventionally prepared InGaAsP / InP Multiple Quantum Well Structure
Fig.2: Cross-sectional TEM images of a conventionally prepared InGaAsP / InP Multiple Quantum Well Structure
Fig.3: High resolution XTEM lattice [110] image of conventional prepared InP

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