Investigation of the Optimum Mg Doping Concentration in p-Type-Doped Layers of InGaN Blue Laser Diode Structures

Abstract

In GaN-based laser diode (LD) structures, Mg doping in p-type-doped layers has a significant influence on the device performance. As the doping concentration increases, the operation voltage decreases, whereas the output power decreases as a result of increased optical absorption, implying that optimization of the Mg doping concentration is required. In this study, we systematically investigated the effect of the Mg doping concentration in the AlGaN electron-blocking layer (EBL) and the AlGaN p-cladding layer on the output power, forward voltage, and wall-plug efficiency (WPE) of InGaN blue LD structures using numerical simulations. In the optimization of the EBL, an Al composition of 20% and an Mg doping concentration of 3 × 1019 cm−3 exhibited the best performance, with negligible electron leakage and a high WPE. The optimum Mg concentration of the p-AlGaN cladding layer was found to be ~1.5 × 1019 cm−3, where the maximum WPE of 38.6% was obtained for a blue LD with a threshold current density of 1 kA/cm2 and a slope efficiency of 2.1 W/A.

Temperature Dependence of Electron Leakage Current in InGaN Blue Light-Emitting Diode Structures

“…For an acceptor doping concentration of N a , the ratio of ionized accepter concentration to N a is given by [ 47 , 48 ] where E Fp , E a , k , and T are the hole quasi-Fermi energy level, acceptor ionization energy, Boltzmann constant, and the absolute temperature, respectively. g a is called a degeneracy factor, which is normally taken as 4 for acceptors.…”

“…The increase in the concentration of ionized Mg acceptors As the temperature increases, the hole concentration in the EBL increases owing to the thermal activation of the Mg acceptors. At room temperature, the ionization ratio of Mg in AlGaN is very low, only a few percent or even less than 1%, because of the large acceptor ionization energy [47]. The ionization ratio of Mg can be increased significantly with increasing temperature, resulting in an increase in the negatively charged Mg acceptor ions with temperature.…”

“…The increase in the concentration of ionized Mg acceptors increases the Coulomb repulsion of electrons, which appears with the increase in the effective potential barrier for electrons. Figure 7a For an acceptor doping concentration of Na, the ratio of ionized accepter concentration a N − to Na is given by [47,48]…”

“…The thermionic model in Equation ( 4) implies that the increase in B φ with increasing temperature is the main reason for the decreased electron leakage current with temperature, despite the increase in the thermal energy of electrons with temperature. Using Equation ( 4), the ratio of the electron leakage current density between temperatures T1 and T2 can be expressed as follows: For an acceptor doping concentration of N a , the ratio of ionized accepter concentration N − a to N a is given by [47,48]…”

Characteristics of an In0.02Ga0.98N QW laser at a 462 nm wavelength

“…In the recent years, InGaN has become probably the most intensively studied among all the material systems used for QW lasers. Although InGaN can emit effectively light in red, green, blue and ultraviolet, recently most InGaN applications focused on the blue [1][2][3][4][5][6] and green [5][6][7][8] spectral ranges (some of them [5][6] can operate, with composition and structure variations, both in blue and green spectra) and also some in the deep violet [9]. In this paper we present simulations of the main characteristics of an InGaN QW laser that operates in the blue spectrum, at the wavelength of 462 nm.…”