Optoelectronic properties of 2-D and 3-D-grown GaInNAs =GaAs QW light emitting diodes and laser diodes J.-M. Ulloa, A. Hierro, J. Miguel-Sanchez, A. Guzman, A. Trampert, J.L. Sanchez-Rojas and E. Calleja Abstract: The optoelectronic properties of light emitting diodes (LEDs) and laser diodes (LDs) based on GaInNAs/GaAs quantum wells (QWs) grown under two-dimensional (2-D) and three- dimensional (3-D) conditions are compared. In spite of the longer wavelength, the 2-D LED shows better luminescence properties than the one with island formation. The broadening of the photocurrent spectra and the Stokes shift are used to analyse carrier localisation effects. The emission from localised states is found to impact the electroluminescence of the 3-D device even at room temperature, while it does not significantly influence the high-temperature emission of the 2-D LED. From a detailed analysis of the low-temperature electroluminescence as a function of injected current, nonradiative recombination is found to be the main carrier recombination mechanism in a wide range of currents in the 3-D LED, while it is very small in the 2-D case. Consequently, defect formation seems to be closely related to the 3-D growth, limiting laser emission in these structures. These results suggest that 2-D-grown GaInNAs/GaAs QWs may be more desirable for achieving laser emission at long wavelengths. 1 Introduction Since GaInNAs was proposed as a suitable material system to achieve laser emission at the 1:3 mm and 1:55 mm optical fibre windows [1], much work has been dedicated to improve the material quality and device performance. GaInNAs=GaAs quantum well (QW) laser diodes emitting at 1:3 mm have been quickly developed [2, 3], but it remains still challenging to achieve high external efficiencies in these devices, and this problem becomes much more pronounced when the wavelength is increased towards 1:55 mm: In order to reach such wavelengths, large N concentrations are needed, leading to strong nonradiative recombination [4]. One possible approach to overcome this problem is the growth of GaInNAs quantum dots (QDs). Room-temperature photoluminescence (PL) peak emission at 1:52 mm has been reported for GaInNAs QDs grown by gas-source molecular beam epitaxy [5], supporting the feasibility of 1:55-mm lasers using these structures. The QD lasers would take advantage of the 3-D carrier confinement, that would improve their optical performance compared to the QW lasers [6]. However, it is still not clear how the QD structures compare to QWs in terms of luminescence properties and efficiency in this material system. In this work, the optoelectronic properties of light emitting diodes (LEDs) and laser diodes (LDs) emitting around 1:3 mm based on GaInNAs=GaAs QWs grown under 2-D and 3-D conditions are compared. The PL, photocurrent (PC) and electroluminescence (EL) spectra are used to evaluate the QW optical quality and to quantify carrier localisation through the Stokes shift. The EL emission is analysed in detail as a function of injected current so as to asses the influence of nonradiative recombination. Rapid thermal annealing (RTA) is used to improve the lumine- scence efficiency of the LDs, and its impact on the QW morphology and LED performance is also addressed. 2 Experimental The samples were grown by molecular beam epitaxy (MBE) on (001) GaAs substrates using Ga, As and In solid sources, and a radiofrequency plasma source for N. The active zone of all the samples consisted of a GaInNAs single QW with 150-nm GaAs barriers. The well width was 70 – 80  A for all the samples, and the In and N contents were nominally  25 –30 and 2 –2:5%; respectively. For comparison, two of the samples were fabricated with comparable simple QW structure, but were grown at different temperatures. The QW grown at the lower temperature showed a perfectly streaky RHEED pattern, indicating 2-D growth [7]. On the contrary, the QW grown at the  25  C higher temperature, was characterised by a spotty pattern as a result of the 3-D growth mode [7, 8]. The 2-D and 3-D morphologies are evident from the cross-sectional dark-field TEM images shown in Fig. 1. In the 2-D case, clear compositional fluctuations are observed along the QW, while flat interfaces are still maintained. A small increase in the growth temperature of  25  C leads to the formation of quasi-3-D islands along the upper interface. Two laser diodes were realised containing the same active zone and grown under the same conditions as the two simple QWs described above. As claddings, 2-mm-thick Al 0:3 Ga 0:7 As layers were q IEE, 2004 IEE Proceedings online no. 20040911 doi: 10.1049/ip-opt:20040911 J.-M. Ulloa, A. Hierro, J. Miguel-Sanchez, A. Guzman and E. Calleja are with the ISOM - Universidad Polite ´cnica de Madrid, Ciudad Universitaria s/n, E-28040 Madrid, Spain A. Trampert is with the Paul-Drude-Institut fu ¨r Festko ¨rperelektronik, Hausvogteiplatz 5-7, D-10117 Berlin, Germany J.L. Sanchez-Rojas is with Dpto. Ingenieria Electronica, Electrica y Automatica, E.T.S.I. Industriales – Campus Universitario, 13071 Ciudad Real, Spain Paper first received 30th April and in revised form 4th June 2004 IEE Proc.-Optoelectron., Vol. 151, No. 5, October 2004 421