Insights into Growth-Oriented Interfacial Modulation within Semiconductor Multilayers.

Interfacial engineering plays a crucial role in regulating the quality and property of heterogeneous structures, especially for nanometer-scaled devices. However, traditional methods for interfacial modulation (IFM) generally treat all the interfaces uniformly, neglecting the inherent disparities of interfaces like their growth sequence. Herein, it is found that the growth-oriented characteristic of IFM strongly determines the main regions where the modulation takes effect. Specifically, in a semiconductor quantum well structure, the arsenic atoms modulated at the well-on-barrier (WoB) interface tend to diffuse into and thus affect the next-grown well layer. In contrast, the arsenic atoms introduced at the barrier-on-well (BoW) interface mainly take effect within the next-grown barrier layer. According to theoretical simulations and electron holography (EH) experiments, the depth of quantum wells and the height of potential barriers are extended by introducing arsenic atoms at WoB and BoW interfaces, respectively. Resultantly, while modulating at the BoW interface has little impact on the photoluminescence (PL) spectrum, applying IFM at the WoB interface could dramatically improve the luminescent intensity (about 30%), which demonstrates the impact of the growth-oriented characteristic. Furthermore, in situ bias EH results indicate that IFM at the WoB interface helps to suppress the quantum-confined Stark effect.

Domino Effect of Thickness Fluctuation on Subband Structure and Electron Transport within Semiconductor Cascade Structures.

Effectively restraining random fluctuation of layer thickness (RFT) during the thin-film epitaxy plays an essential part in improving the quality of low-dimensional materials for device application. While it is already challenging to obtain an ideal growth condition for thickness control, the tangle of RFT with interfacial problems makes it even more difficult to guarantee the properties of heterostructures and the performance of devices. In our research, the RFT of potential barriers and wells within a semiconductor multilayer is demonstrated to correlate with the interfacial grading effect (IFG) and to affect the band offset strongly. Then, the synergetic effect of RFT and IFG that serves as the first domino is shown to impact the subband structure and the electron transport successively. On the basis of an investigation of a quantum cascade structure, statistical results indicate a normal distribution of RFT with a standard deviation of about 1 Å and an extreme value of 3 Å (about one monolayer) for all the layers within 38 cascade periods. The "seemingly negligible" RFT could actually reduce the conduction band offset for tens to hundreds of meV and alter the subband gaps at a rate of 40 meV/monolayer at most. Furthermore, the dependence of different subband gaps on the barrier/well thickness differs from one another. In addition, the distribution of wave function could also be regulated dramatically by RFT to change the type of electron transition and thus the carrier lifetime. Further impacts of RFT and the RFT-modulated subband alignment on electron transport result in two different mechanisms (injection-dominant and extraction-dominant) of electron population inversion (PI), which is manifested by comparatively discussing the results of in situ electron holography and macro performances.

Control of electron tunnelling by fine band engineering of semiconductor potential barriers.

Quantum tunnelling (QTN) devices show a promising future for energy saving and ultrafast operation thanks to the unprecedented development of two-dimensional materials. However, the immature techniques for device fabrication hamper severely their further progress and application. To overcome such a challenge, the abundant processing technology used in semiconductor electronics is worth considering. Herein, a device prototype is fabricated based on band engineering to enable flexible control of QTN probability (TP) within a III-V semiconductor multilayer. While the initial heights of all barriers are set to obtain similar TPs under no bias, the conduction band slopes of InGaSb and AlSb barriers are modulated to a state where their TPs vary reversely under electric fields. On this basis, revealed by in situ bias electron holography, a unidirectional accumulation of electrons has been realized inside the multilayer structure. Moreover, the inevitable element segregation/diffusion during device growth plays a key role in band structure optimization, which is confirmed by strain analysis. The feasibility of the above modulation strategy is also confirmed by theoretical simulations. Our findings might provide a new perspective on the innovation of semiconductor devices and the application of QTN effect.

Heterointerface-Driven Band Alignment Engineering and its Impact on Macro-Performance in Semiconductor Multilayer Nanostructures.

Interfaces in semiconductor heterostructures is of continuously greater significance in the trend of scaling materials down to the atomic limit. Since atoms tend to behave more irregularly around interfaces than in internal materials, accurate energy band alignment becomes a major challenge, which determines the ultimate performance of devices. Therefore, a comprehensive understanding of the interplay between heterointerface, energy band, and macro-performance is desiderated. Here, such interplay is explored by investigating asymmetric heterointerfaces with identical fabrication parameters in multiple-quantum-well lasers. The unexpected asymmetry derives from the atomic discrepancy around heterointerfaces, which ultimately improves the optical property through altered valence band offsets. Strain and charge distribution around heterointerfaces are characterized via geometric phase analysis and in situ bias electron holography, respectively. Combining experiments with theories, arsenic-enrichment at one of the interfaces is considered the origin of asymmetry. To reveal actual band alignment, valence band model is modified focusing on the transition around heterojunctions. The enhanced photoluminescence intensity reflects the alleviation of hole confinement insufficiency and the enlargement of valence band offset. The results help to advance the understanding of the general problem of interface in nanostructures and provide guidance applicable to various scenarios for micro-macro correlation.