2DEG Properties of AlScN/GaN and AlYN/GaN HEMTs Determined by Terahertz Optical Hall Effect

Vallery Stanishev^1,2*Isabel Streicher^3,4Alexis Papamichail²Viktor Rindert¹Plamen P. Paskov²Stefano Leone³Vanya Darakchieva¹

• ¹Lund University, Lund, Sweden
• ²Linköping University, Linköping, Östergötland, Sweden
• ³Fraunhofer Institute for Applied Solid State Physics IAF, 79108 Freiburg, Germany
• ⁴Consiglio Nazionale delle Ricerche - Istituto per la Microelettronica e Microsistemi (CNR-IMM), Strada VIII n. 5 - Zona Industriale, onsiglio Nazionale delle Ricerche - Istituto per la Microelettronica e Microsistemi (CNR-IMM), Strada VIII n. 5 - Zona Industriale, 95121 Catania, Italy

We present a contactless determination of the two-dimensional electron gas (2DEG) properties in AlScN/GaN and AlYN/GaN high electron mobility transistor (HEMT) structures using the Terahertz Optical Hall Effect (OHE) over a temperature range of 20 K to 360 K. The structures are grown on sapphire or 4H-SiC substrates by metalorganic vapor phase epitaxy (MOCVD) and feature ∼ 10-nm thick barrier layers with Sc and Y contents ranging from 4.6% to 17.3% and 3.3% to 8.2%, respectively. The temperature dependencies of the 2DEG density and mobility parameters are analyzed and discussed in a comparative manner. Additionally, conclusions are drawn regarding the predominant scattering mechanisms at both low and room temperatures. Furthermore, the 2DEG effective mass parameter m * in AlScN/GaN and AlYN/GaN is determined for the first time. At low temperatures m * is found to be in the range 0.20 -0.27 m 0 , close to the value of 0.23 m 0 for bulk GaN. As temperature increases above 100 K, m * gradually rises reaching 0.33 -0.39 m 0 at room temperature, consistent with findings for AlGaN/GaN HEMTs.The underlying causes of this temperature-dependent increase in effective mass are discussed, with a possible explanation linked to polaron effects and deviations from the classical Drude model.