Study of GeSn based heterostructures: towards optimized group IV MQW LEDs

Abstract

We present results on CVD growth and electro-optical characterization of Ge(0.92)Sn(0.08)/Ge p-i-n heterostructure diodes. The suitability of Ge as barriers for direct bandgap GeSn active layers in different LED geometries, such as double heterostructures and multi quantum wells is discussed based on electroluminescence data. Theoretical calculations by effective mass and 6 band k∙p method reveal low barrier heights for this specific structure. Best configurations offer only a maximum barrier height for electrons of about 40 meV at the Γ point at room temperature (e.g. 300 K), evidently insufficient for proper light emitting devices. An alternative solution using SiGeSn as barrier material is introduced, which provides appropriate band alignment for both electrons and holes resulting in efficient confinement in direct bandgap GeSn wells. Finally, epitaxial growth of such a complete SiGeSn/GeSn/SiGeSn double heterostructure including doping is shown.

Direct bandgap type-I GeSn/GeSn quantum well on a GeSn- and Ge- buffered Si substrate

“…[1][2][3][4][5][6][7][8][9] The successful demonstration of direct bandgap GeSn light emitting diodes (LEDs), and optically-pumped GeSn lasers, [10][11][12][13][14] indicates the great potential of GeSn for Si-based light sources. GeSn LEDs with double heterostructures (DHS) 11,[15][16][17][18][19][20][21][22] and quantum wells (QWs) [23][24][25][26][27][28][29][30][31] have been reported. It is generally acknowledged that the QW structures could be applied to the LEDs and lasers to improve their device performance.…”

“…It is generally acknowledged that the QW structures could be applied to the LEDs and lasers to improve their device performance. LEDs based on the Ge/GeSn/Ge QW structure have been demonstrated, 27 whose detailed analysis suggested that using Ge as a barrier did not provide the desired carrier confinement, and thereupon use of the ternary material SiGeSn as the barrier was proposed, since the bandgap energy and lattice constant of SiGeSn alloys can be tuned independently. The SiGeSn/GeSn/SiGeSn QWs were grown and characterized recently.…”

“…The similar phenomenon was also reported elsewhere. 27 Since the penetration depth of the 532-nm laser is only ∼20 nm, 38 the major absorption occurs only in the GeSn top barrier. To verify the optical transitions in the QW, a 1550-nm CW laser (penetration depth of ∼900 nm) with 500 mW power and 24 µm spot size was used as the pumping source.…”

GeSn lasers for CMOS integration

“…In contrast to the band alignment with Ge barriers, the GeSn/SiGeSn configuration offers a clear Type-I band alignment, confining both electrons and holes inside the well. Holes of the GeSn/Ge structure are more confined in the barrier than in the well [6]. In the GeSn/Ge structure the holes actually pile up in the barrier, rather than in the well layers.…”

(Si)GeSn nanostructures for light emitters

“…While room temperature electroluminescence at low current densities from homojunction light emitting diodes (LEDs), relying on the direct band gap, has already been demonstrated [6][7][8][9] , optically-pumped lasers still suffer from low maximum operating temperatures 3 . Those may be overcome by decreasing the residual compressive strain in the device by more elaborate geometries, like under-etched micro-disk resonators, or by using quantum effects in heterostructures, where charge carriers are confined in a quantum well or a quantum dot 10,11,12 .…”