Liquid Phase Epitaxy (LPE) has been a critical technique for the growth of high-quality infrared (IR) and terahertz (THz) materials, particularly mercury cadmium telluride (HgCdTe) and indium antimonide (InSb). These materials are essential for advanced detector applications due to their tunable bandgaps and superior optoelectronic properties. LPE offers precise control over composition and defect density, making it a preferred method for producing high-performance epitaxial layers.

The LPE process involves the deposition of a crystalline layer from a supersaturated liquid solution onto a substrate. For HgCdTe growth, the liquid phase typically consists of Hg, Cd, and Te, while InSb growth involves In and Sb. The substrate is brought into contact with the melt, and controlled cooling ensures the epitaxial layer forms with the desired composition and thickness. The key advantage of LPE is its near-equilibrium growth conditions, which minimize defects and improve crystal quality compared to other techniques like Molecular Beam Epitaxy (MBE) or Chemical Vapor Deposition (CVD).

Composition control in HgCdTe is achieved by adjusting the melt composition and growth temperature. The CdTe mole fraction (x) in Hg₁₋ₓCdₓTe determines the cutoff wavelength of the material, which is critical for IR detection. Precise control over x is necessary to tailor the bandgap for specific applications, such as short-wave infrared (SWIR), mid-wave infrared (MWIR), or long-wave infrared (LWIR) detection. LPE allows for reproducible composition gradients by carefully managing the cooling rate and melt stoichiometry. For example, a cooling rate of 0.1–0.5°C/min is often used to achieve uniform HgCdTe layers with x values ranging from 0.2 to 0.6, corresponding to cutoff wavelengths between 3–12 µm.

Defect density in LPE-grown materials is significantly lower than in films produced by other methods. The near-equilibrium growth conditions reduce point defects, dislocations, and other structural imperfections that degrade detector performance. In HgCdTe, the primary defects are Hg vacancies, which can be minimized by optimizing the Hg partial pressure during growth. Post-growth annealing in a Hg-rich atmosphere further reduces vacancy concentrations to below 10¹⁵ cm⁻³. InSb grown by LPE exhibits low dislocation densities (< 10³ cm⁻²) due to the close lattice match between the epitaxial layer and the substrate, typically InSb or GaAs with a buffer layer.

The advantages of LPE for IR and THz materials are numerous. First, the technique produces high-purity layers with excellent electronic properties, including high carrier mobility and low noise. For HgCdTe, electron mobilities exceeding 10⁵ cm²/V·s have been reported at low temperatures, making it ideal for high-sensitivity detectors. Second, LPE allows for thick layer growth (up to 50 µm), which is beneficial for absorbing long-wavelength IR radiation. Third, the process is relatively cost-effective compared to MBE or CVD, as it does not require ultra-high vacuum systems or complex gas-phase reactions.

Despite its advantages, LPE has some limitations. The growth of large-area uniform layers can be challenging due to convective instabilities in the melt. Additionally, the technique is less suitable for heterostructures with abrupt interfaces compared to MBE. However, for bulk-like epitaxial layers of HgCdTe and InSb, LPE remains a highly effective method.

In summary, LPE is a well-established technique for growing high-quality IR and THz materials with precise composition control and low defect densities. Its near-equilibrium growth conditions produce superior electronic properties, making it indispensable for advanced detector applications. While newer techniques like MBE offer advantages in interface control, LPE continues to be a reliable and cost-effective method for producing HgCdTe and InSb epitaxial layers.

The continued refinement of LPE processes, including improved melt homogenization and temperature control, will further enhance the quality of these materials. Future developments may focus on scaling up production while maintaining the high crystalline perfection that makes LPE-grown HgCdTe and InSb indispensable for infrared and terahertz technologies.