M. Ahoujja

Two‐dimensional electron gas properties of AlGaN/GaN heterostructures grown on 6H–SiC and sapphire substrates

High quality Al0.15Ga0.85N/GaN heterostructures have been fabricated on 6H–SiC and sapphire substrates by metalorganic vapor phase epitaxy (MOVPE). A temperature independent mobility, indicative of the presence of a two‐dimensional electron gas (2DEG), was observed in all samples below 80 K. The highest low temperature 2DEG mobility, 7500 cm2/V s, was measured in AlGaN/GaN grown on 6H–SiC; the sheet carrier density was 6×1012 cm−2. Strong, well resolved, Shubnikov–de Haas oscillations were observed in fields as low as 3 T and persisted to temperatures as high as 15 K. Hall effect measurements also revealed the presence of well‐defined plateaus in the Hall resistance. The high quality 2DEG properties of the AlGaN/GaN heterostructures grown on 6H–SiC are attributed to the absence of significant parallel conduction paths in the material.

HIGH CARRIER LIFETIME INSB GROWN ON GAAS SUBSTRATES

We report on the growth of near bulklike InSb on GaAs substrates by molecular beam epitaxy despite the 14% lattice mismatch between the epilayer and the substrate. Structural, electrical, and optical properties were measured to assess material quality. X-ray full widths at half-maximum were as low as 55 arcsec for a 10 μm epilayer, peak mobilities as high as ∼125 000 cm2/V s, and carrier lifetimes up to 240 ns at 80 K.

Interface roughness scattering in thin, undoped GaInP/GaAs quantum wells

Electronic transport properties of very thin undoped GaInP/GaAs quantum wells have been measured by temperature dependent low field Hall effect and by Shubnikov–de Haas effect. Strong Shubnikov–de Haas oscillations were observed after increasing the electron concentration via the persistent photocurrent effect. Low temperature mobilities of up to 70 000 cm2/V s at carrier concentrations of 6.5×1011 cm−2 were observed in a 20 A quantum well. The results are compared with the theory of interface roughness scattering which indicates extremely smooth interfaces; however, discrepancies between experiment and theory are observed.

Multiple subband population in delta-doped AlAsSb/InGaAs heterostructures

We have measured the Shubnikov–de Haas (SdH) effect in δ-doped AlAs0.56Sb0.44/In0.53Ga0.47As heterostructures and observed a population of the second subband. Using the persistent photoconductivity effect we increased the electron density from 26.73 to 28.20×1011 cm−2 in the first subband and 6.61 to 7.20×1011 cm−2 in the second. The onset of the second subband population occurs when the first subband is filled to a density of 11.56×1011 cm−2. From the nonparabolic band approximation we calculated the effective masses in both subbands before illumination. The effective mass for the second subband was evaluated using the temperature dependence of the SdH amplitude. Its value agrees well with the values obtained from the k⋅p approximation and infrared cyclotron resonance measurements.

Persistent photoconductivity in thin undoped GaInP/GaAs quantum wells

Persistent photoconductivity has been observed at low temperatures in thin, unintentionally doped GaInP/GaAs/GaInP quantum wells. The two‐dimensional electron gas was studied by low field Hall and Shubnikov–de Haas effects. After illumination with red light, the electron concentration increased from low 1011 cm−2 to more than 7×1011 cm−2 resulting in an enhancement of both the carrier mobility and the quantum lifetime. The persistent photocarriers cannot be produced by DX‐like defects since the shallow dopant concentration in the GaInP layers is too low to produce the observed concentration. We suggest that the persistent carriers are produced by photoionization of deep intrinsic donors in the GaInP barrier layer. We also report observation of a parallel conduction path in GaInP induced by extended illumination.

Multi-layer conduction in epitaxial InSb grown on GaAs substrates

Electron transport properties of molecular beam epitaxy grown InSb on GaAs substrates are studied using the conventional Hall effect and the mobility spectrum technique. The latter technique reveals the existence of at least three different conducting channels in InSb. Our analysis of the Hall data and the mobility spectrum shows that the conduction in InSb is determined by a highly dislocated interfacial layer between the InSb layer and the GaAs substrate, a high mobility bulk-like InSb layer, and, possibly, a surface layer.