We present all-monolithic. single-step grown, room-temperature, electrically-pumped vertical cavity lasers at 1.55pm based on 111-As compounds, with threshold current density of 570A/cmz, differential quantum efficiency greater than 50% and threshold voltage of 3V. We employed three active regions, epitaxially stacked in series with Esaki-junctions to increase the gain and the differential efficiency.The development of monolithic 1.55pm vertical-cavity surface-emitting lasers (VCSELs) has been hampered by the lack of readily available highly reflective Distributed-Bragg-Reflectors (DBRs). However, it is possible to achieve lasing with lass reflective DBRs by epitaxially stacking multiple active regions and increasing the gain. Such a VCSEL could also exhibit high differential quantum efficiencies well exceeding unity, as has been demonstrated at YXOnm.' Previously reported VCSELs at this wavelength. either by epitaxy or fusion, has been limited to differential quantum efficiencies no more than 15%.2' 3, A fully lattice matched, all-epitaxial design circumvents any reliability issues related to fused junctions or metamorphic mirrors, which is critical for mass production.Good DBRs using Sb-based compounds have been reported, and we have recently demonstrated the first roomtemperature, electrically-pumped 1.55pm VCSEL with low threshold current densities employing such DBRs? However, it is still desirable to develop VCSELs based on more readily available 111-As compounds and the prospects of obtaining q<, > 1 is appealing for nnmerous applications. Furthermore, it is desirable to grow the entire structure in a single step. As illustrated in Figure 1, VCSELs presented here employ 35 and 45 periods of latticematched Alo.~Gao.~~Ino.s~A~A/Alo.eInn,~~As DBRs grown on n-InP. The bottom output mirror is calculated to he 98.4% reflective and the gold-coated top mirror. 99.8%. ,/The active region consists of three p-i-n'stages of AlIdCaAs strain-compensated quantum wells connected in series by Esaki-junctions (doped C and Si)placed at the nulls of the mode in a 2-h cavity (Figure 2). We have previously reported on the scaling properties,.of the gain and the differential efficiency of 1 . 5 5 p edge-emitters employing such stacked-active-regions! The modal gain scales sub-linearly and the differential efficiency linearly with the number of active stages. Thus, the differential efficiency is limited to 300%, which would occur in an absorptionless cavity, and can be tailored by controlling the mirror reflectivity.The Esaki-junction grown between the last active region stage allows use of top DBR that is also doped n-type. Since the free-carrier absorption is more than factor of two greater for the p-type than the n-type, this scheme is useful in reducing the optical loss. Since the Esaki-junctions are thin enough to be placed at the nulls of the mode without adding significant additional losses. As we show, these junctions, when designed proper$, need not introduce significant voltage drop either. Suchtechnique has been applie...