N. Blanco

Interface quality study of ECR-deposited and rapid thermal annealed silicon nitride Al/SiNx:H/InP and Al/SiNx:H/In0.53Ga0.47As structures by DLTS and conductance transient techniques

Abstract In this article, we study the influences of the rapid thermal annealing temperature and dielectric composition on the electrical characteristics of ECR-deposited silicon nitride SiN x :H–InP and SiN x :H–InGaAs interfaces. C–V , deep level transient spectroscopy (DLTS) and conductance transient analysis have been applied. As for InP cases, DLTS results reveal that rapid thermal annealing application increases interfacial state density. In contrast, transient conductance measurements show that disorder induced gap-state (DIGS) damage density diminishes when RTA is applied. So, we can conclude that RTA treatments take out the insulator damage to the interface. In the InGaAs-n cases, we have observed that DIGS damage evolution with RTA temperature is opposite to the interfacial state density. This behaviour seems to suggest some temperature activated defect exchange between the insulator and the interface. Finally, as for the insulator composition influence on the interface quality of the InGaAs-n samples, DLTS results suggest that the intermediate x values (1.43 and 1.50) provide better interfaces than extreme x values. Conductance transient measurements add complementary information: insulator damage increases when x increases. Hence, x =1.43 seems to be the best choice to improve the overall interface quality.

Evidence of phosphorus incorporation into InGaAs/InP epilayers after thermal annealing

We report on Raman scattering measurements on annealed In0.53Ga0.47As/InP layers that reveal the outdiffusion of phosphorus from the substrate and its possible incorporation in substitutional positions in the In0.53Ga0.47As lattice. Raman signal associated with InP-like modes was detected in the annealed samples. The effect is also observed in samples where the substrate was protected by a SiNx:H capping and were annealed in arsenic atmosphere, thus ruling out the possibility of a surface contamination by atmospheric phosphorus evaporated from the InP substrate. Protruding regions of a few microns were observed on the surface, which were identified as misoriented In1−xGaxP and InP crystals by means of micro-Raman measurements.

Study of Si+-implanted and annealed InP by means of Raman spectroscopy

Abstract We have carried out a Raman scattering study of the lattice damage produced by 150 keV Si+ implantation in InP and the subsequent lattice recovery by rapid thermal annealing (RTA). The Raman spectra show that for implantation doses usually employed for producing n-type InP, the sample is fully amorphized by the implantation. The degree of lattice recovery achieved by RTA at different temperatures in the range between 300°C and 875°C is also studied. The observation of a strong TO mode in the samples annealed at the lower temperatures indicates the existence of polycrystalline and/or misoriented regions. Second-order Raman scattering is used to obtain a more accurate estimation of the crystalline recovery, which is found to be highest for RTA at 875°C for 10s.

Study of the electrical activation of Si + -implanted InGaAs by means of Raman scattering

Raman scattering has been used to study the lattice recovery and electrical activation of Si+-implanted In0.53Ga0.47 As achieved by rapid thermal annealing. The degree of crystallinity recovery of totally amorphized samples is studied for annealing temperatures between 300 and 875 °C. A good degree of recovery is achieved for an annealing temperature of 600 °C. Higher annealing temperatures are required to electrically activate the Si donors. The observed LO phonon-plasmon coupled modes allow us to monitor the electrical activation by means of Raman scattering. We find that electrical activation sets in for annealing temperatures around 700 °C, and gradually increases up to an annealing temperature of 875 °C. The optimal conditions for the rapid thermal annealing are found to be 875 °C for 10 s.

Lattice damage study of implanted InGaAs by means of Raman spectroscopy

Abstract We have studied by means of Raman scattering the crystallinity loss induced by ion-beam implantation in the InxGa1−xAs alloy lattice matched to InP. Si+ was implanted at 150 keV with fluences in the 1012 – 5×1014 cm−2 range. The Raman scattering signatures of implantation-induced disorder and the progressive amorphization of the InxGa1−xAs crystal are discussed. With increasing implantation dose, the GaAs-like LO mode exhibits a gradual intensity reduction and an asymmetric broadening, while a broad peak emerges at low frequencies corresponding to the activation by the induced disorder of transverse acoustic modes. The Raman scattering measurements have allowed us to check the full amorphization of the In0.53Ga0.47As for a Si+ implantation dose of 5×10 14 cm −2 .

Low interface trap density in rapid thermally annealed Al/SiNx:H/InP metal–insulator–semiconductor devices

A minimum interface trap density of 1012 eV−1 cm−2 was obtained on SiNx:H/InP metal–insulator–semiconductor structures without InP surface passivation. The SiNx:H gate insulator was obtained by the electron cyclotron resonance plasma method. This insulator was deposited in a single vacuum run and was composed of two layers with different nitrogen-to-silicon ratios. The first layer deposited onto the InP was grown with a nitrogen-to-silicon ratio of N/Si=1.55, whereas the second one was grown with a N/Si ratio of N/Si=1.43. After the insulator deposition, rapid thermal annealing of the devices was performed at a constant annealing time of 30 s. The interface trap density minimum value was obtained at an optimum annealing temperature of 500 °C. Higher annealing temperatures promote thermal degradation of the interface and a sharp increase in the trap density.

Comparison of Raman-scattering and Shubnikov-de Haas measurements to determine charge density in doped semiconductors

We have verified the accuracy of free-charge determinations from Raman scattering in doped semiconductors by comparing the results obtained from phonon-plasmon coupled-mode line-shape fits with the charge-density values extracted from the analysis of the Shubnikov-de Haas oscillations. The experiments were carried out on n-InP layers, and conduction band nonparabolicity was included both in the Lindhard-Mermin model used to fit the Raman spectra and in the Shubnikov-de Haas analysis. We find a very good agreement between Raman and magnetotransport results, which confirms the reliability of the charge-density determination from Raman-scattering measurements when the line-shape analysis is carried out using the Lindhard-Mermin model.

Generalization of the hydrodynamical model to analyze Raman scattering by free carriers: application to n-InP

Abstract The results of free-carrier density evaluation by means of Raman scattering in doped semiconductors strongly depend on the electric susceptibility model used to calculate Raman line shapes. Although the Lindhard–Mermin model has proved to yield accurate results over a wide range of free-charge densities, it involves a fair amount of numerical calculations, and simpler though less accurate models such as the Drude and the hydrodynamical models are widely used. We propose an extension of the hydrodynamical model in which nonparabolicity and temperature effects are taken into account. The resulting extended model retains the simplicity of the hydrodynamical model and yet it improves significantly the agreement with the results of the Lindhard–Mermin model.

MICRO-RAMAN STUDY OF SURFACE ALTERATIONS IN InGaAs AFTER THERMAL ANNEALING TREATMENTS

We present a micro-Raman study of alterations in InGaAs/InP epilayers after rapid thermal annealing. Defects consisting of protruding material with typical dimensions of a few microns can be observed on the surface of the annealed samples. Micro-Raman measurements on these defects show that they consist of InxGa1-xP alloys, suggesting that phosphorus diffusion from the InP substrate occurs during the RTA cycle. The defect-free region of the epilayer is also altered leading to the formation of an In1-xGaxAs1-yPy quaternary alloy.