Both direct and indirect transitions of photoluminescence and electroluminescence are observed in a Ge n+p diode. The relative intensity of direct radiative recombination with respect to indirect radiative recombination increases with the increase in the optical pumping power, injection current density, and temperature. The increase in electron population in the direct valley is responsible for the enhancement. The spectra can be fitted by the combination of direct and indirect transition models. The direct radiative transition rate is ∼1600 times of the indirect transition, estimated by electroluminescence and photoluminescence spectra near room temperature.

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High-quality epitaxial Ge films were grown on GaAs substrates by ultrahigh vacuum chemical vapor deposition. High crystallinity and smooth surface were observed for these films by x-ray diffraction, transmission electron microscopy, and atomic force microscopy. Direct band gap emission (1550 nm) from this structure was detected by photoluminescence. Valence band offset of 0.16 eV at the Ge/GaAs interface was measured by x-ray photoelectron spectroscopy. N-type arsenic self-doping of 1018/cm−3 in the grown Ge layers was determined using electrochemical capacitance voltage measurement. This structure can be used to fabricate p-channel metal-oxide-semiconductor field-effect transistor for the integration of Ge p-channel device with GaAs n-channel electronic device.

This paper describes the structural and electrical properties of Al 2 O 3 thin films grown through atomic layer deposition onto Ge substrates over a wide deposition temperature range ͑50-300°C͒. From grazing-incidence X-ray reflectivity and X-ray photoelectron spectroscopy, we found that increasing the deposition temperature improved the Al 2 O 3 film density and its dielectric stoichiometry; nevertheless, dielectric intermixing between main Al 2 O 3 and interfacial GeO 2 appeared at temperatures above 200°C, along with degradation of the GeO 2 /Ge interface. Accordingly, a relatively large gate leakage current ͑J g ͒ and a high density of interfacial states D it ͑Ͼ10 13 cm −2 eV −1 ͒ were observed as a result of deterioration of the entire Al 2 O 3 /Ge structure at higher deposition temperatures. In addition, although subsequent high-temperature processing at 600°C in a N 2 ambient could relieve the oxygen-excessive behavior further, i.e., to provide a more stoichiometric film, the accompanying GeO x volatilization close to the dielectric interface caused greater damage to the electrical performance. Only forming gas annealing ͑H 2 /N 2 , 1:10͒ at low temperature ͑300°C͒ improved the capacitance-voltage characteristics of the Pt/Al 2 O 3 /Ge structure, in terms of providing a lower value of D it ͑ca. 6 ϫ 10 11 cm −2 eV −1 ͒, a lower value of J g , and a reduced hysteresis width.

We studied the thermal stability of the as-deposited HfO x N y thin films on the Ge substrate by employing rapid thermal annealing. After undergoing high-temperature processing, we observed several interesting physical and electrical features presented in the HfO x N y /Ge system, including a large Ge out-diffusion ͑Ͼ15 atom %͒ into high-k films, positive shift of the flatband voltage, severe charge trapping, and increased leakage current. These phenomena are closely related to the existence of GeO x defective layer and the degree of resultant GeO volatilization. We abated these undesirable effects, especially for reducing the amount of Ge incorporation ͑Ͻ5 atom %͒ and the substoichiometric oxide at dielectric-substrate interface, through performing NH 3 plasma pretreatment on the Ge surface. These improvements can be interpreted in terms of a surface nitridation process that enhanced the thermal stability of the high-k/Ge interface. In addition, we measured that the conductance loss in inversion was still high and it revealed independence with respect to gate bias, reflecting the fact that the minority carriers in Ge can rapidly respond either through a diffusion mechanism or through midgap trap states residing in Ge bulk substrates.