I was carrying out the in-situ RHEED intensity oscillation measurements during growth of Ge on reconstructed Si(111) substrate inside the MBE chamber. Substrate temperature was maintained at ~ 300 deg C. From the calibration of the thickness monitor (QCM) using Rutherford backscattering spectrometery (RBS) method, I have found growth rate of Ge was ~ 2.5 ML / minute.
Due to latiice mismatch ~ 4 % among the Ge/Si system, for growth of first few monolayers, oscillation of the RHEED spot (corresponding to the diffraction from the Ge(111) plane) is expected.
In contrast, I have observed damped (nearly exponential) behaviour of the intensity of the Ge(111) diffraction spot.
What are the possible reasons for such behaviour of intensity of the RHEED spot ?
Hi Anjan, one point is that the growth rate depends on both, orientation and layer thickness and tends to stagnate initially, before it converges towards the thick-layer limit. So you may not get any growth for a quite a while, in particular at such low growth temperature as you used. If the diffraction spots then die out rapidly this indicates surface roughening, which for {111} surfaces differs from {100} surfaces. Attached a recent paper we wrote (will appear in print in December issue of Journal of Mcroscopy but the preprint is already online). Yours, Thomas
Dear Mr. T. Walther and Mr. M. Jankowski,
It seems that, for the present growth condition of Ge on Si(111) from the early stage of thin film growth, both the layer and islands of Ge are forming concurrently. Hence, in the evolution of Ge(111) TED spot with time, the indication of layered growth of Ge for first few monolayers is not prominently visible because of 3D roughening.
In my earlier case, growth of Ge has been taken place with a rate ~ 2.5 monolayers/min. So, I plan to repeat the similar measurements with reduction of Ge flux rate which will increase the time duration for formation of Ge thin film and possibility of prominent RHEED intensity oscillation.
With best regards,
Anjan
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