Pulsed Operation of Cleaved-Facet InGaN Laser Diodes
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ABSTRACT Blue-emitting nitride laser diodes have been fabricated on a-plane sapphire (I 120). The active region is composed of 10 In,18Ga.82N quantum wells, which were grown by MOCVD at atmospheric and low pressure in a modified two-flow Thomas-Swan Ltd. horizontal reactor. The chemical precursors used were trimethylgallium (TMGa), trimethylindium (TMIn), trimethylaluminum (TMAI), ammonia, and disilane. The n- and p-contacts were formed by depositing Ti/Al/Ni/Au and Ni/Au/Ni/Au, respectively. Diode wafers were thinned to less than 50 jtim before they were cleaved along the sapphire r-plane (1102). Lasers show TE polarization, spectral line narrowing, and far field interference patterns above the lasing threshold. The laser emission spectra peak at 410-420 nm. Under pulsed2 operation at room temperature, the lowest observed threshold current density was 15 kA/cm with threshold voltages ranging from 50-90 V. Differential efficiencies are as high as 7% with maximum output powers greater than 50 mW. Near and far field mode patterns are presented. Structures are gain-guided devices with each device occupying a mesa with a width of 125 gtm. Device widths range from 3 to 20 gm, with lengths of 500 to 1200 gtm. INTRODUCTION ifI-nitride based diode lasers have been fabricated by several research groups [1-8]. These devices are believed to have applications in high-density digital versatile disk (HD-DVD) systems, in high resolution laser printers, in pollution monitoring, and in medical surgery. Recent lifetime estimates of 10,000 h. for CW lasers based on epitaxially laterally overgrown (ELO) technology by Nakamura show that the material can be made robust enough to live up to commercial lifetime requirements [1]. Most of the lasers that have been reported have facets that were formed by C12 based reactive ion etching (RIE). However, cleaved facets are favored in commercial device manufacturing because of the reproducibility of the cleaving process and its independence from processing parameters to which etched facets are subject [7]. Sapphire is not as easy to cleave as many other rn-v materials because there are many cleave planes within close angular proximity. Despite this difficulty, we confirm in this article that cleaving is a viable technology for nitride laser fabrication as was previously reported by Nakamura [8]. EXPERIMENT In this article, we report pulsed operation of cleaved-facet rn-nitride lasers with lasing wavelengths ranging from 410 to 420 nm. The epitaxial layer structure is shown in Figure 1. This laser structure was grown on an a-plane (1120) sapphire substrate which were grown by 1197
Mat. Res. Soc. Symp. Proc. Vol. 482 © 1998 Materials Research Society
metal-organic chemical-vapor deposition (MOCVD) at atmospheric and low pressure in a modified two-flow Thomas-Swan Ltd. horizontal reactor. The chemical precursors used were trimethylgallium (TMGa), trimethylindium (TMIn), trimethylaluminum (TMA1), ammonia (NH 3), and disilane (Si 2H6), bis(cyclopentadienyl) magnesium (Cp2Mg). Growth w
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