Optical gain in semiconductors

Shaklee, K. L.; Nahory, R. E.; Leheny, R. F.

doi:10.1016/0022-2313(73)90072-0

Cited by 366 publications

(193 citation statements)

References 23 publications

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“…Table S3 in SI). The modal gain g, which includes waveguide losses is determined for four different excitations from 38 Fig. 3c; a differential gain of (0.40 ± 0.04) cm/kW is obtained from the slope.…”

Section: Direct Bandgap Group IV Materials May Thus Represent a Pathwmentioning

confidence: 99%

Lasing in direct-bandgap GeSn alloy grown on Si

et al. 2015

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Direct bandgap group IV materials may thus represent a pathway towards the monolithic integration of Si-photonic circuitry and CMOS technology.Although a group IV direct bandgap material has not been demonstrated yet, silicon photonics using CMOS-compatible processes has made great progress through the development of Si-based waveguides 12 , photodetectors 13 and modulators 14 . The thus emerging technology is rapidly expanding the landscape of photonics applications towards tele-and data communication as well as sensing from the infrared to the mid infrared wavelength range 15-17 . Today's light sources of such systems are lasers made from direct bandgap group III-V materials operated off-or on-chip which requires fibre coupling or heterogeneous integration, for example by wafer bonding 3 , contact printing 4,5 or direct growth 6,7 , respectively. Hence, a laser source made of a direct bandgap group IV material would further boost lab-on-a-chip and trace gas sensing 15 as well as optical interconnects 18 by enabling monolithic integration. In this context, Ge plays a prominent role since the conduction band minimum at the -point of the Brillouin-zone (referred to as -valley) is 3 located only approx. 140 meV above the fourfold degenerate indirect L-valley. To compensate for this energy difference and thus form a laser gain medium, heavy n-type doping of slightly tensile strained Ge has been proposed 19 . Later, laser action has been reported for optically 20 and electrically pumped Ge 21 doped to approx. 1 and 4×10 19 cm -3 , respectively. However, pump-probe measurements of similarly doped and strained material did not show evidence for net gain 22 , and in spite of numerous attempts, researchers failed to substantiate above results up to today. Other investigated concepts concern the engineering of the Ge band structure towards a direct bandgap semiconductor using micromechanicallystressed Ge nanomembranes 9 or silicon nitride (Si 3 N 4 ) stressor layers 23 . Very recently, Süess et al. 10 presented a stressor-free technique which enables the introduction of more than 5.7 % 24 uniaxial tensile strain in Ge µ-bridges via selective wet under-etching of a pre-stressedlayer. An alternative technique in order to achieve direct bandgap material is to incorporate Sn atoms into a Ge lattice, which primarily reduces the gap at the -point. At a sufficiently high fraction of Sn, the energy of the -valley decreases below that of the L-valley. This indirect-to-direct transition for relaxed GeSn binaries has been predicted to occur at about 20 % Sn by Jenkins et al. 25 , but more recent calculations indicate much lower required Sn concentrations in the range of 6.5-11.0 % 26,27 . A major challenge for the realization of such GeSn alloys is the low (< 1 %) equilibrium solubility of Sn in Ge 28 and the large lattice mismatch of about 15 % between Ge and -Sn. For GeSn grown on Ge substrates, this mismatch induces biaxial compressive strain causing a shift of the  and L-valley crossover towards higher Sn concentrations ...

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Section: Direct Bandgap Group IV Materials May Thus Represent a Pathwmentioning

confidence: 99%

Lasing in direct-bandgap GeSn alloy grown on Si

et al. 2015

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“…The PL is detected for several stripe lengths. From these data the modal gain can be deduced [15,16]. For guaranteeing success of the VLS method, saturation effects have to be avoided.…”

Section: Resultsmentioning

confidence: 99%

Optical properties and modal gain of InGaN quantum dot stacks

Kalden

Sebald

Gutowski

et al. 2009

Phys. Status Solidi (c)

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We present investigations of the optical properties of stacked InGaN quantum dot layers and demonstrate their advantage over single quantum dot layer structures. Measurements were performed on structures containing a single layer with quantum dots or threefold stacked quantum dot layers, respectively. A superlinear increase of the quantum dot related photoluminescence is detected with increasing number of quantum dot layers while other relevant GaN related spectral features are much less intensive when compared to the photoluminescence of a single quantum dot layer. The quantum dot character of the active material is verified by microphotoluminescence experiments at different temperatures. For the possible integration within optical devices in the future the threshold power density was investigated as well as the modal gain by using the variable stripe length method. As the threshold is 670 kW/cm 2 at 13 K, the modal gain maximum is at 50 cm -1 . In contrast to these limited total values, the modal gain per quantum dot is as high as 10 -9 cm -1 , being comparable to the II-VI and III-As compounds. These results are a promising first step towards bright low threshold InGaN quantum dot based light emitting devices in the near future.

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“…The optical pump intensity dependent PL measurement was performed by controlling pump beam intensity using calibrated glass slides as neutral density filters. The variable stripe length method [5] was used to measure the optical gain of the structure. Optical re-absorption measurements were performed by varying the separation of excitation spot location and the emission edge of the sample [6].…”

Section: Methodsmentioning

confidence: 99%

Superluminescence in Green Emission GaInN/GaN Quantum Well Structures under Pulsed Laser Excitation

et al. 2007

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We report nonlinear optical investigation of green emission GaInN/GaN multi-quantum structures grown along c-and m-axes on sapphire and bulk GaN substrates, respectively. Under intense pulsed photo excitation, we observed strong superluminescence near the lasing condition in c-plane grown quantum well structures with full width at half maximum of 6 nm. The superluminescence couples out of the edge of the sample in a mode pattern consistent with gain in a high mode of the waveguide. The wavelength of the superluminescence is 474 nm. The threshold intensity of superluminescence was found to be 156 kW/cm 2 . Increasing pump intensity leads to a strong photoluminescence blueshift as large as 380 meV in samples grown along the c-axis on sapphire substrate, while under the same excitation conditions, the blue shift for the m-axis grown structure on bulk GaN substrate is less than 10 meV. The large emission blueshift is hereby attributed to the internal piezoelectric field in the c-axis grown structure. Its absence in the m-axis structure could enable low threshold current visible laser diodes.

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Optical gain in semiconductors

Cited by 366 publications

References 23 publications

Lasing in direct-bandgap GeSn alloy grown on Si

Lasing in direct-bandgap GeSn alloy grown on Si

Optical properties and modal gain of InGaN quantum dot stacks

Superluminescence in Green Emission GaInN/GaN Quantum Well Structures under Pulsed Laser Excitation

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