(a) Growth rate of N-face InN as a function of growth temperature for N-limited growth (N ). The data points were determined from thickness measurements by cross-section SEM, exemplified for three different temperatures: (b) , (c) , and (d) . Note the decrease in InN thickness with increasing temperature and the accumulation of In droplets in (d).
(a) In desorption measured by QMS during InN decomposition in a temperature range between 560 and (insets show typical RHEED patterns on each side of the desorption maximum); (b) closeup view of the In desorption in the high-temperature region III: (c) Arrhenius presentation of In desorption over yielding two activation energies of (low ) and (high ).
(a) In desorption of ML In adsorbed on a N-face GaN surface at different temperatures. The steady-state desorption (after closure of the In shutter) represents the maximum desorption of In (i.e., droplet boundary), yielding (b) an activation energy of when plotted as a function of .
(Color online) (a) Evaluation of the net In accumulation rate on the surface by balancing (1) the rate of thermal decomposition from bulk InN “to” the surface (blue curve) with (2) the rate of maximum In desorption “from” the surface (black curve). The difference between the two curves yields (b) a surface structure diagram for impinging In flux vs substrate temperature (In adsorption), showing a small region where an In adlayer can be formed on the surface and a large region of In droplet formation.
(Color online) (a) Determination of the net In accumulation rate on the surface for the growth case showing (1) the rate of thermal decomposition from bulk InN, i.e., the In loss from the SEM growth rate analysis (blue curve) and (2) the rate of maximum In desorption “from” the surface (black curve). Similar to Fig. 4, the difference between the two curves allows to construct (b) a growth structure diagram for actual growth conditions (i.e., impinging In flux at constant N flux versus growth temperature). Three characteristic growth surface structures can be achieved: one dry no-adlayer terminated surface, one In adlayer stabilized surface, and one consisting of In droplets on top of the adlayer. Growth is found unsustainable at temperatures above .
and (insets) AFM micrographs of thick InN layers grown on N-face freestanding GaN templates with (a) GaN buffer layer, under conditions of constant temperature but variable In fluxes of (b) (dry N-rich regime), (c) (In-adlayer N-rich regime), and (d) (In-droplet regime). The height scale of the images is and for the images is .
(a) Variation of the RHEED specular intensity during the nitrogen consumption of various different In surface coverages at . (b) Time period of RHEED intensity oscillation as a function of adsorbed In coverage pointing to a saturated In adlayer coverage of 1 ML. The oscillation time is defined by the time span between onset of oscillation and last inflection point in the differentiated RHEED intensity.
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