Fig. 3: In situ Raman and RHEED of gallium selenide samples.

a Scatter plot of Raman measurement positions in parameter space, with the marker color indicating the Ga₂Se₃ to GaSe ratio. The filled contour plot bounded by the white-dashed line also shows the Ga₂Se₃ to GaSe ratio, calculated only for samples where gallium selenide grows in a 3D mode. The background heatmap provides a qualitative extrapolation of the contour plot (refer to Supplementary Note 1 for the employed equation). The colorbar is omitted for both the contour plot and background heatmap as these are intended to illustrate trends, with quantitative values indicated by the marker colors. b Boxplot of Ga₂Se₃ to GaSe ratios derived from Raman data, categorized by three distinct morphologies. The red line indicates the sample’s median, while the box represents the interquartile range (IQR). The whiskers extend up to 1.5 times the IQR, with outlier points shown as white dots. c Scatter plot of the grown samples as a function of T_sub and Φ_Se/Ga, with markers color-coded by RHEED pattern type (e.g. streaky, spotty + rings). The classification of RHEED patterns was performed algorithmically using a Histogram of Oriented Gradients (HOG)-based method (see main text). The accompanying dendrogram illustrates the clustering of similar RHEED patterns based on shape features: streaky patterns (light blue, indicative of 2D planar growth) and spotty/ring patterns (light yellow, associated with mixed or 3D growth). d Scatter plot of lattice constant as a function of T_sub and Φ_Se/Ga, extracted from RHEED after 3 min of growth for all runs. The red line represents the literature lattice constant of GaSe, with the gray box showing a ± 0.5% deviation. The dashed blue line indicates the mean lattice constant across all samples. The error bars are extracted from the uncertainties in the fitted peak positions.