RHEED oscillations

Using the RHEED oscillation technique, Grandjean et al has demonstrated the in-situ control of the In composition in InxGai.xN grown by MBE [14],... 

RHEED oscillations are also particularly useful in monitoring the type of growth mode of the depositing material. Four different film growth modes are generally identified mainly related to the diffusion coefficient of the adatoms on the surface, the dimensions of the substrate terraces, and the lattice parameter mismatch between the substrate and the film ... 

A common phenomenon observed upon adsorption of molecules is the decrease in the elastic peak intensity as a function of coverage. Figures 15A, B show the intensity and angular width of the elastic peak as a function of HCN coverage on Pd. The intensity correlates well with layer formation on the surface, much like RHEED oscillations. Even though the scattering mechanism is decidedly dipolar , the... 

EgeUioff WF, Jacob I (1998) Reflection high-energy electron-diffraction (RHEED) oscillations at 77 K. Phys Rev Lett 62(8) 921-924... 

Figure 11.13 A typical example of (hypothetical) RHEED oscillation data during MBE growth at a rate of 1 monolayer/sec. Note that the surface is roughening during the 8 mono-layers of deposition as shown by the decay of the oscillations but upon termination of growth the surface becomes smooth and the intensity recovers. To obtain this type of behavior the experiment is configured in the off-Bragg condition so that alternate monolayers of the film interfere destructively. This type of oscillation is observed in the intensity of all reflected and diffracted beams. The most intense is the specularly-reflected beam so that is the one normally used.

In films that grow 2D for many layers, intensity oscillations have been observed for certain growth conditions using RHEED and LEED. Observation is made by monitoring the intensity of a diffracted beam as a function of time during growth. The period of an oscillation corresponds to the time it takes to deposit a monolayer. In practice, oscillations are ffequendy used to calibrate deposition rates. 

While kinematic difffacdon theory describes intensity oscillations adequately in some cases, there are problems with it when it is used to analyze RHEED measurements. The period of the oscillations is correcdy predicted, but not necessarily the phase. In spite of these complications, intensity oscillations are evidence for periodic changes in the siuface structure. 

In the process of MBE, the surface structure can be investigated by reflected high energy electron diffraction (RHEED). During MBE growth, one often observes an oscillation in the intensity of the specular reflected beam as a function of time. This is interpreted to be due to the layer-by-layer growth of a two-dimensional island. 

A. Daniluk, P. Mazurek, K. Paprocki, P. Mikolajczak. RHEED intensity oscillations observed during the growth of YSi2 t on Si(lll) substrates. Surf SciSQl 226, 991. 

The RHEED technique has recently been used successfully in the in-situ compositional control of the MBE growth of InxGai.xN, 0 < x < 0.4 [12], This was achieved by monitoring the oscillations of the specular beam intensity during deposition of the alloy. 

A simple interpretation/use of the RHEED data is essentially based on the RHEED intensity oscillation that allows monitoring the crystal layer thickness. 

A complete interpretation of the RHEED intensity oscillations is not so straightforward. In feet, when STO is grown block-by-block by PLD or evaporation, the oscillation intensity reproduce the number of unit cells but when STO is grown by... 

The RHEED analysis allows identifying the different film growth modes. In the step-flow and layer-by-layer growth modes, the RHEED pattern maintains the 2D typical features, but only in the second case it is possible to observe the periodical RHEED spot intensity oscillations without any damping. In the island growth mode, there is a quite pronounced damping of the RHEED intensity and, consequentiy, a disappearing of the RHEED intensity oscillations. 

Wood, C.E.C. (1981) RHEED intensity oscillations during MBE of GaAs. Surf ScL, 108, L441 L443. 

Haeni, J. et al (2000) RHEED intensity oscillations for the stoichiometric growth of SrTiOs thin films by reactive molecular beam epitaxy. 

Figure4.24 RHEED intensity oscillations during initial growth of4H-AlN on 4H-SiC (1100).

A 500ftm X 30 lm excitation stripe was used. Thickness values were determined from RHEED pattern intensity oscillations. (After Ref [141].)... 

Figure 11.10 A schematic of the diffiaction patterns in a RHEED experiment resulting from different surface structures. To simplify the drawing the broad rods of the rough surface are drawn as constant in width. Properly, for a two-level surface they have two non-zero Fourier coefficients and should oscillate as sine waves perpendicular to the surface. Therefore the rods should be wdder and narrower along their length. See Figure 11.11 for a more accurate representation.

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