Each semiconductor has a direct and an indirect band gap; whichever is lower determines the nature of the band gap. The band gap is a property of the lattice constant; the band gap can be changed by varying the lattice constant. The lattice constant can be changed by various ways, e.g by applying pressure by heating or cooling or by mixing with another semiconductor. Both the direct and the indirect band gap will change with the lattice constant but at different rates. Hence there is a possibility that at a certain lattice constant, the direct band gap becomes lower than the indirect band gap; in that case the semiconductor will behave as a direct bad gap semiconductor.

One can convert direct band gap into an indirect one by using an action opposite to that converting Si nanocrystals into a direct band gap material, namely, by applying compressive strain. See S. H. Tolbert et al., Phys. Rev. Lett. 73, 3266 (1994): In this work the authors induce indirect band gap in (direct semiconductor) CdSe nanocrystals using external compressive strain.

ধন্যবাদ Md. Atikur Rahman সুন্দর আলোচনা ও সূত্র উল্লেখ করবার জন্য।

Hi Dear M.A.Hadi,

In order to convert an indirect bandgap material M1 into a direct bandgap material, the simplest way is a chemical method consisting in alloying it with a direct bandgap material M2 with similar physico-chemical properties.

The resulting material M1(1-x)M2(x) is not exactly the same as the initial one M1, but it can become a direct energy bandgap at a certain alloy composition xcritical retaining some of the properties (main ones) of the initial material M1.

- As an example: if we mix AlAs (an indirect bandgap)with GaAs(a direct energy bandgap) then we obtain an alloy AlxGa1-xAs which becomes a direct energy bandgap at x

Dear Prof. Abderrahmane Kadri ,

As-salamu-alaikum. Thank you very much for nice discussion with example. May Allah save you, your family and your countrymen along world peoples.

Allah hafez,

M.A. Hadi

Dear Dr M.A. Hadi,

You are welcome.

May Allah save you too, your family, your contryland people and the whole humanity from all around the world from this CoVid-19 disease tragedy.

Best regards,

Prof A. Kadri

To Abderrahmane Kadri

May Allah grant your prayer. Amin.

Hi Dear M.A. Hadi,

As to your question about how to turn an indirect energy bandgap into a direct one, there is a very good example I would like to add: the seminal example of GaAs(1-x)Px which is an indirect bandgap material at x>0.45 with no quantum efficiency. Thanks to the fine work done by M.G. Craford and collaborators (see for instance M.G. Craford, ''Recent developments in LED technology'' IEEE Trans. Electron devices, ED 24, 935 (1977) and references therein) GaAs(1-x)Px material (with x>0.45) was turned to a ''virtual direct energy bandgap material'' by doping with nitrogen. Here nitrogen impurities introduced in GaAsP behave as isoelectronic deep trap centers resonant in the continuum of the conduction band. These isoelectronic deep trap centers behave as radiative recombination centers able to trap an electron from the conduction band of GaAsP and a hole from its valence band, then making them to recombine and the energy gained in this process is transformed in a photon in the visible electromagnetic range, ranging from red in GaAs(1-x)Px at x=0.4, orange (x=0.65), yellow (x=0.85), and green (x=1.0). This very nice work made it possible to realize and obtain the 1st high quantum efficiency visible LED's based on III-V solid state semiconductors (see reference by M.G. Craford above). Here, N-doped GaAs(1-x)Px does not become a real direct energy bandgap, but Notrogen introduces a ''virtual'' state resonant (deep trap center resonant state) in the continuum of the conduction band acting just as a ''milestone'' direct bandgap.

Dear Prof. Abderrahmane Kadri,

As-salamu-alaikum. Thanks again for another nice discussion with example. May Allah save His creations on the earth from Coronavirus and any others epidemic.

Allah hafez,

M.A. Hadi

Dear Dr M.A. Hadi,

Thank you very much,

You are welcome.

Prof. A. Kadri

Thank you Salah Daoud for answering. Is it applicable for theoretical process?

Thanks again Dr. Salah Daoud for providing a reference paper.

Best regards,

M.A. Hadi

There are some common ways to convert indirect to direct band gap materials. As for example doping, pressure and temperature. But which one or all applicable depend on materials under investigation

Thank you M N H Liton for answering. After pressure release and cool down, what will be happened? Do they remain direct band gap materials? Best of luck. Stay safe by the grace of almighty Allah.

Thank you Dr. Rafid A. Abdullah for providing a useful link. Stay safe by the grace of almighty Allah.

Best regards,

M.A. Hadi

I am following...

Both Direct and indirect bandgap can be changed by external or internal forces. Such forces can change the bandgap configuration of materials and thereby change a direct to indirect or vice versa.

Thank you Abdolmohammad Ghalambor Dezfuli for adding an answer.

Most of the semiconductors have a direct and an indirect band gap. Doping (heavy and light), pressure and temperature can help to convert an indirect material to direct one by altering the lattice constant of the material.

The following link may help you.

https://doi.org/10.1021/acsomega.9b02655

see the following link:

https://www.egypttoday.com/Article/1/95782/Egyptian-scientist-wins-Physics-World-2020-Breakthrough-of-the-Year