Tuning Optical Properties of GaN-Based Nanostructures by Charge Screening

Abstract

In this paper we will show the influence of doping and free charge screening of polarization fields on the optical and electronic properties of GaN-based nanostructures. Modulation-doped nanostructures can be used to enhance the oscillator strength of the fundamental transition energy. The free charge and doping are shown to be an additional degree of freedom for GaN-based device design.1. Introduction Nitride-based nanostructures are nowadays used in both electronic and optoelectronic devices. In the first case, the large energy gap of GaN-related semiconductors allows for the building of high power devices with high breakdown voltages and high thermal conductivity. In the optoelectronic context, nitride materials are employed in blue emitters (LED and lasers) and in photodetection. The design of such structures is, however, complicated by the presence of internal polarization field, which induces a high junction field when a heterojunction between different nitride semiconductors is formed. The polarization field is the sum of piezoelectric polarization and spontaneous polarization [1]. There are several macroscopic manifestations of the polarization field; among them, the large Stark shift of the fundamental optical transition and the reduction of the oscillator strength of the fundamental optical transition for large wells are very crucial in any optical application of nitride materials.In the case of nitride-based heterojuntion devices, fix (doping) and free charges should be considered in the determination of the real electric field in the heterostructure. In fact, for the case of doping, the polarization field can ionize the donor (or acceptor) thus producing opposite charge that screens (partially) the bare polarization field [2]. The same screening of the polarization field arises when free charges (electrons and holes) are injected into the heterostructure. These charges form a dipole counterbalancing the polarization field [3].We should point out that fix and free charges can be tailored by a proper choice of growth condition, for the doping, and by selecting a proper operation point (such as bias, current, optical pumping etc.) for the free charge. Thus, optical and electronic properties of nitride-based nanostructures can be tuned by using two new degrees of freedom: doping and free charges.Experimentally, it has been established for both and AlGaN/ GaN [12][13][14] heterostructures that doping of the active region produces a strong modification of the optical properties, namely: (i) a blue-shift of the photoluminescence (PL) peak, (ii) an enhancement of the emission intensity, (iii) a reduction of the laser

Bandgap tunable Zn3-3Mg3N2 alloy for earth-abundant solar absorber

“…Starting from 2000, GaN has become one of the most important semiconductors after Si [5]. It is no wonder that it finds ample application in LED lighting and displays of all kinds, lasers, detectors, and high-power amplifiers.…”

“…By using equations (2-18b) and (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), an expression for absorption coefficient in terms of the bandgap energy is found by [115] ℎ…”

“…This result confirms that the higher the Mg concentration, the weaker the diffractive peak is. Atomic force microscopy (AFM) was performed on selected sputtered Zn3N2 and Zn2.46Mg0.54N2 films (see figure [5][6]. AFM observations suggest that the Zn3N2 and Zn0.246Mg0.54N2 have a columnar morphology with column widths of 100 nm and 200 nm, respectively.…”

“…The Mg 3s orbital energy is significantly higher than the Zn 4s orbital energy, and thus the CBM of Mg3N2 should be higher than that of Zn3N2. Therefore, I think that the bandgap variation with alloying results mainly from the shift in the position of the conduction band (see figure [5][6][7][8][9][10][11][12][13]. Further study is needed to confirm this explanation.…”

Performance Comparison of Electrical Parameter between GaNFinFET and Si-FinFET Nano Devices

“…We have seen that GaN channel is more useable than silicon channel. The GaN has wide band gap of 3.4 eV affords its special properties for applications in optoelectronic high-power and highfrequency devices [1] [2]. GaN is a very hard (12±2 GPa [3]), mechanically stable wide bandgap semiconductor material with high heat capacity and thermal conductivity [4], but we have found that the GaN is better channel material than Si-FinFET.…”