Influences of the spacer layer growth temperature on multilayer InAs∕GaAs quantum dot structures

Abstract

The growth temperature of spacer layers (SPLs) is investigated as a means to obtain identical layers for multilayer quantum dot (QD) structures. A 5-layer 1.3-μm InAs∕GaAs QD structure with 50-nm GaAs SPLs served as a model system. It is found that the growth temperature of the GaAs SPLs has pronounced effects on both the structural and optical properties of the InAs QDs. For GaAs SPLs grown at a low temperature of 510°C, dislocations are observed in the second and subsequent layers, a result of significant surface roughness in the underlying spacer layer. However by increasing the growth temperature to 580°C for the final 35nm of the 50-nm GaAs SPLs, a much smoother surface is achieved, allowing the fabrication of essentially identical, defect free QD layers. The suppression of defect formation enhances both the room-temperature photoluminescence efficiency and the performance of 1.3-μm multilayer InAs∕GaAs QD lasers. An extremely low continue-wave room-temperature threshold current density of 39A∕cm2 is achieved for an as-cleaved 5-layer device with emission at 1.306μm and ground state operation up to 100°C.

Improved temperature performance of 1.31-/spl mu/m quantum dot lasers by optimized ridge waveguide design

“…The temperature was then decreased back to 510 C for the growth of the next DWELL. Areal dot densities of cm per layer were measured by atomic force microscopy on uncapped structures [4], [5]. The energy separation between ground and excited state transitions for this sample, as measured by PL spectroscopy, was 50 meV.…”

The role of high growth temperature GaAs spacer layers in 1.3-/spl mu/m In(Ga)As quantum-dot lasers

“…However, stacking multiple QD layers modifies the growth of subsequent layers, which in the extreme results in defect formation as a consequence of the increasing amount of strained material deposited. Solutions include strain compensation [3], [4], removal of the largest dots by selective evaporation [5], and the use of high growth temperature spacer layers (HGTSLs) between QD sheets, which have recently been demonstrated to greatly enhance device characteristics in multilayer 1.3-m In(Ga)As QD lasers [6], [7]. This letter describes the measurement of gain and loss of five-layer QD laser material with and without HGTSLs to reveal the mechanisms responsible for this improvement.…”

A novel approach to increase emission wavelength of InAs/GaAs quantum dots by using a quaternary capping layer

“…This GaAs layer is grown at an ele− vated temperature (590 o C), and is called a high growth tem− perature spacer layer (HGTSL). At this temperature, gal− lium adatoms have a high mobility which leads to plana− rising the growth front for subsequent layers [3,14]. It has been shown that a GaAs HGTSL can planarise QD growth front only if its thickness is greater than a critical limit [15,16].…”