A. Arnoult

Ordered magnetic phase in Cd1-xMnxTe/Cd1-y-zMgyZnzTe : N heterostructures: magnetooptical studies

Photoluminescence magnetospectroscopy is employed to examine the low-temperature magnetic phase that is induced by the carrier-mediated ferromagnetic exchange interaction in modulation-doped Cd1-xMnxTe quantum well. Unusual properties of the domain structure are linked to tendency towards spin-density wave formation in this low-dimensional magnetic system

Nitrogen doping of Te-based II–VI compounds

Abstract We report on the doping properties of the II–VI Te-related compounds, ZnTe, CdTe and CdZnTe, CdMgTe and ZnMgTe, using two different nitrogen plasma sources. High doping levels are measured for ZnTe, slightly lower for CdTe (8 × 10 17 cm −3 ). Following the comparative study of nitrogen doping in these materials, we invoke the possible formation of nitride compounds as responsible for the large nitrogen amount incorporated in Mg-containing alloys. The formation of such compounds might be reduced by using appropriate growth conditions and doping levels in the 4 × 10 17 cm −3 range are obtained in ternary and quaternary alloys containing Mg. Such doping levels allow the growth and the study of high-quality modulation-doped heterostructures.

Interdiffusion mechanisms in CdTe/CdMgZnTe:N modulation-doped heterostructures

p-type modulation doping of CdTe–CdMgZnTe heterostructures, using nitrogen as a dopant, induces a strong interdiffusion of the quantum wells. Photoluminescence, secondary ion mass spectrometry, and x-ray diffraction measurements give a coherent description of the interdiffusion process: the destruction of the quantum wells occurs essentially by exchange of Cd and Mg atoms across the interface, while the Zn atoms stay in their lattice sites. We show that the presence of nitrogen at the interface, which enhances the interdiffusion, is related to the diffusion of nitrogen and not to segregation. Additional mechanisms are observed at higher doping.

Absorption and emission in n type II–VI quantum wells

Abstract The evolution of the optical properties as a function of 2D electron concentration n e is studied using CdTe quantum wells. The trion absorption peak evolves to the Fermi edge singularity (FES) as the exciton peak progressively disappears. The splitting between these two peaks is linear in n e . This is explained in the framework of Hawrylaks theory of the many-body optical response of free carriers. The emission spectra show a transformation similar to that observed for gated electron gases and previously attributed to a metal–insulator transition. There is, however, a contradiction with the absorption results which can be explained in terms of a Fermi sea of electrons over the whole range of densities.

Ferromagnetic transition induced by a two-dimensional hole gas in a semimagnetic quantum well

The presence of a ferromagnetic transition in single, modulation-doped quantum wells of Cd 1 - x Mn x Te/ Cd 1-y-z Mg y Zn z Te : N is evidenced by magnetospectroscopy. The transition is driven by long-range RKKY interaction between the Mn spins, mediated by the two-dimensional hole gas. Magneto-optic data are well described in terms of a mean-field model. The value of the exchange-field induced by the spin-polarized hole gas is determined. We show that the zero-field splitting which characterizes the ferromagnetic order contains both a p-d exchange term and a contribution due to hole hole exchange interactions. The initial hole polarization is only partial and increases slowly when the temperature is reduced further below the transition.

Oscillator strengths of charged excitons: combining magnetoabsorption and photoluminescence dynamics in semimagnetic quantum wells

We present a systematic study of the oscillator strength of the positively charged excitons (X+) in Cd1-xMnxTe quantum wells. CW-absorption and time-resolved photoluminescence measurements were combined as two approaches for the determination of the oscillator strength. By varying (in a small magnetic field) the spin subband hole distribution at constant total concentration, we observe an increase of the oscillator strength in absorption, proportional to the hole concentration in one spin subband (the one which allows the X+ formation). The measurements done for different, total hole concentrations show an important decrease of the X+ oscillator strength per carrier when increasing the total concentration. On the contrary the radiative lifetime, measured in time-resolved PL experiment, is found to be constant over the whole range of hole gas concentrations, and equal to the value which we deduce from transmission in the limit of vanishing hole concentration

Semimagnetic Semiconductors in Studies of Charged Excitons

Negatively or positively charged excitons in semiconductors, also known as trions, were studied theoretically by Lampert [1] already in the fifties. However, the first experimental observation of charged excitons by Kheng et al.[2] in modulation n-doped CdTe/CdZnTe multiple quantum wells (MQWs) occurred more than thirty years later. Formation of an experimentally detectable complex by three carriers was made possible due to the enhancement of their mutual interaction by confining them in a quantum well. The observation of Kheng et al. was rapidly followed by experimental evidence for negatively and positively charged excitons in III-V and II-VI semiconductor quantum structures [3–5].

Nitrogen doping of Te-based II-VI heterostructures

Abstract The growth conditions and the electrical properties of modulation-doped Cd1−xMnxTe/Cd1−y−zMgyTe:N (0 ⩽ × ⩽ 0.05) quantum well structures, in which a ferromagnetic transition has been observed, are presented. The growth temperature, the design of the structure and the composition of layers must be controlled with a greater care than in undoped samples. Ohmic contacts have been realised on a single quantum well structure by growing a composition graded layer at the surface.