ARTICLE pubs.acs.org/JPCC
Thermodynamic Behavior of Excitonic Emission Properties in Manganese- and Zinc-Codoped Indium Phosphide Diluted Magnetic Semiconductor Layers Sejoon Lee,†,‡ Emil B. Song,‡ Kang L. Wang,‡ Chong S. Yoon,§ Im Taek Yoon,† Yoon Shon,*,† and Tae Won Kang*,† †
Quantum-Functional Semiconductor Research Center, Dongguk UniversitySeoul, Seoul 100-715, Korea Department of Electrical Engineering, University of California at Los Angeles, Los Angeles, California 90095, United States § Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea ‡
ABSTRACT: The thermodynamic behavior of excitonic emission properties in manganese- and zinc-codoped indium phosphide (InMnP:Zn) diluted magnetic semiconductor (DMS) layers was investigated. Compared to the InMnP:Zn DMS layer (Mn ≈ 0.06%), the inhomogeneous thermal-broadening of the excitonic-emission line-width in InMnP:Zn DMS layer (Mn ≈ 0.29%) is dominant at lower temperatures. This is attributed to the increase of ionized impurity scattering from Mn ions and results in the increase of excitonphonon coupling strength. As a consequence, high Mn content can lead to low excitonic emission efficiency, although generally a larger Mn content is favorable to increase the Curie temperature of a DMS material.
1. INTRODUCTION The diluted magnetic semiconductor (DMS) has emerged as the most promising candidate for spintronic applications.17 In the past decade, numerous theoretical and experimental studies on the physical properties of DMSs have been extensively conducted in IIIV systems (GaAs, InAs, GaN, and InP).829 Furthermore, in recent years, spintronic devices such as spin field-effect transistor and spin-polarized light-emitting diode (spin-LED) have been experimentally demonstrated.4,5 Although multiple spin functionalities have been observed, the devices show extremely low efficiency. For spin-LED, the electroluminescence efficiency is low and is strongly affected by the spinlifetime and excitonic properties. While the spin-lifetime depends on the ferromagnetic property of the DMS, the excitonic emission relies on the interactions with phonons. Since DMSs generally require low temperature growth conditions to suppress cluster formation, the crystallinity becomes poor compared to conventional semiconductors, and thus results in an increased excitonphonon interaction. Moreover, the magnetic dopants responsible for ferromagnetism in DMSs are intimately correlated with the excitonic emission property. In this work, we examine the thermodynamic behavior of excitonic emission properties in manganese- and zinc-codoped indium phosphide (InMnP:Zn) DMS layers by temperaturedependent photoluminescence (PL) measurements below the ferromagnetic transition temperature (TC). The excitonphonon interaction is analyzed by comparing the experimental PL parameters with theoretical models, which takes into account both the BoseEinstein statistics30 and Fr€ohlich interaction.31 r 2011 American Chemical Society
2. EXPERIMENTAL SECTION The 3-μm thick p-type Zn-doped InP epilayers with hole concentration of >1018 cm3 were grown on semi-insulating (001) InP substrates by metalorganic chemical vapor deposition (MOCVD) using trimethylindium (TMIn), diethylzinc (DEZn), and phosphine (PH3) sources at 650 °C. After deoxiding the sample surface at 500 °C, high purity Mn (99.9999%) was evaporated onto the p-InP:Zn epilayers by molecular beam epitaxy (MBE) in ultra high vacuum (∼1010 Torr) at room temperature for 30180 s. Then, the samples were subsequently annealed at 300 °C for 30 min in N2. After thermal annealing, the thicknesses of InMnP:Zn DMS layers were confirmed to be ∼3050 nm by Auger electron spectroscopy. The InMnP:Zn epilayers showed p-type conductivity with hole concentration of ∼1019 cm3 from Hall effect measurements at room temperature. Structural and microstructural properties of InMnP:Zn epilayers were monitored by high-resolution X-ray diffraction (HR-XRD) and transmission electron microscopy (TEM) measurements, respectively. Temperature-dependent PL measurements were carried out using a 75 cm monochromator with an RCA31034 photomultiplier tube and an excitation HeNe laser source of 632.8 nm at 10100 K. In order to investigate the effect of Mn content on the excitonic properties, two types of InMnP: Zn DMS layers (Mn ≈ 0.06% and ≈ 0.29%) showing clear ferromagnetism (TC ≈ 100150 K)22 were examined in this Received: August 16, 2011 Revised: October 19, 2011 Published: October 21, 2011 23564
dx.doi.org/10.1021/jp207879b | J. Phys. Chem. C 2011, 115, 23564–23567
The Journal of Physical Chemistry C
ARTICLE
Figure 2. PL spectra of (a) IMP-A and (b) IMP-B at 10 K. The red, green, blue, and cyan lines are the best-fitted curves. Figure 1. Bright-field TEM images and SAED patterns of (a) IMP-A (scale bar = 100 nm) and (b) IMP-B (scale bar = 100 nm). XRD spectra of (c) IMP-A and (d) IMP-B.
study. And, for convenience, we denote the two samples as IMP-A (Mn ≈ 0.06%) and IMP-B (Mn ≈ 0.29%). The Mn contents of both samples were confirmed by X-ray photoelectron spectroscopy.
3. RESULTS AND DISCUSSION Figure 1 shows bright-field TEM images of IMP-A and IMP-B. The IMP-A shows no visible particles; however, the IMP-B contains numerous particles with the size of
