Reflection High-Energy Electron Diffraction (RHEED) is a surface-sensitive structural characterization technique that probes the crystallographic order of a surface by directing a high-energy electron beam (5-30 keV) at a glancing angle (1-5°) to the sample surface and recording the resulting diffraction pattern on a phosphor screen or CCD camera. The grazing incidence geometry makes RHEED compatible with in-situ monitoring during thin-film deposition, particularly molecular beam epitaxy (MBE).

Why RHEED Matters in Semiconductor Manufacturing: RHEED provides real-time, in-situ crystallographic monitoring during epitaxial growth, enabling atomic-layer-level control of film thickness, composition, and structural quality that is critical for advanced heterostructure device fabrication.

• Growth mode monitoring — RHEED patterns distinguish growth modes in real time: streaky patterns indicate smooth 2D (layer-by-layer) growth, spotty patterns indicate 3D island (Volmer-Weber) growth, and chevron patterns indicate faceted surfaces • RHEED oscillations — Specular spot intensity oscillates with a period of exactly one monolayer during layer-by-layer growth, providing real-time thickness measurement with atomic-layer precision and growth rate calibration to ±1% • Surface reconstruction tracking — RHEED monitors surface reconstruction changes during growth (e.g., GaAs 2×4 → 4×2 transition indicates As-rich to Ga-rich surface), guiding substrate temperature and flux ratio optimization • Strain relaxation detection — The transition from 2D streaks to 3D spots during strained layer growth pinpoints the critical thickness for strain relaxation, essential for SiGe, InGaAs, and III-N heterostructure design • Interface quality assessment — RHEED pattern sharpness and intensity at each interface during superlattice growth provides real-time feedback on interface abruptness and roughness accumulation

RHEED is the essential real-time structural monitoring tool for epitaxial thin-film growth, providing atomic-layer-precision thickness measurement, growth mode identification, and surface structure feedback that enables the precise control of composition, thickness, and interface quality required for state-of-the-art semiconductor heterostructure devices.