InGaAsP versus InGaAlAs

Most of semiconductor devices used in optical communication networks are made of InGaAsP material. It has since became obvious that devices made of InGaAsP have lower performance due to high thermal sensitivies of this material. Huge effort to find material that will replace the incumbent InGaAsP has been deployed.

Thermal sensitivity of InGaAsP is written in its band structure. It has smaller conduction band-offset allowing thermally activated carriers to escape easily into barriers, and larger valence band offset inhibiting quick carrier emptying. There are many suitable candidates one of them being InGaAlAs which have larger conduction band offset and smaller valence band offset compared to InGaAsP. The race to depose the incumbent InGaAsP is on with new exotic materials such as dilute Nitrides, Bismides and many more...

A Trip to Natural History Museum in New York

As the Snow mountains melt in New York, i headed for the Natural History Museum from Columbus Avenue, just as stone throw to the museum. Large crowd amassed outside ready to get in..People from different nations and ages gathered outside in the morning chill from very cold breeze blowing from the Central Park across the road.

"How Much is the fee to get in", i asked the lady in uniform at the reception desk.

"Well the entry is by donation you can pay any amount but preferred amount is this much for adults and this much for kids".

I pulled out 10 bucks and she asked "how much you want pay", I felt that was enough for everything i was about to see in this vast building with vast collection of different artefacts..the hours came and went while i was gazing at amazing exhibits and never felt the urge to go back to the Broadway Street.

Photocurrent Measurement of Quantum Well Device

We can obtain information about the device structure using photocurrent measurements. As the word photocurrent suggest the measurement involves the use of light to excite electrons for valence band to conduction band by absorption of photons by the electrons. As absorption in semiconductor is determined by the density of photons, density of electrons in valence band and density of empty states in conduction band. if the incident photon has energy larger than bandgap, electron absorbing it will be excited to the conduction band and this is current generation and can be detected using very sensitive equipment such as lock-in amplifier in my case SR830. if we run negative bias across the device the amount of photons with lower energies absorbed increases. Therefore we can determine the bandedge and hence use this feature in Modulators. It is interesting to observe an absorption peak just below the bandedge due to the presence of excitons. The presence of excitons is important feature for Modulators exploiting Quantum Confined Stark Effect.

Finally I get what i was looking for

Photocurrent Measurement can be seen as easiest of experiments to do..i beg to differ especially when dealing with lots of unknowns such as devices which have defects. You will spend days probing but you won't get what you are looking for...But perserverance pays big time.. i have never seen beautiful spectrum like the one i saw today.. I can see excitonic states at work, excitation between energy levels in quantum well as well as the barrier materials...so today is exciting day for me...i can see electrons in the valence band gobbling up incoming photons and get very excited such that they jump over the band gap (that is absorption). while sending in photons of increasing energy (from higher wavelength (low energy) to lower wavelength (higher energy)), electrons get busy absorbing incoming photons and jump to create photo-induced current.

Why trees are Mostly Green and many other colours

Everywhere you go you will find variety of colours on tree leaves. Majority being Green but some are yellow, and many other fantastic colours. I remember my science teacher in primary school telling me that they use that colour to capture the energy from the sun for photosynthesis...Was she right? Dear readers this is my question to you i have alternative explanation but will want to hear from you first..

The Collapse of Heinsenberg Uncertainty Principle

Heinsenberg postulated that we can never measure two entities time and space simultenously. This principle has withstood many scientific tests and it testifies the motion of electrons being randomness such that we can never for sure point the specific position electron in specific time. Many experiments have been performed and failed to dissaprove the claim.
My thought in this principle is that we need to observe the electrons at electron's perspective. if we slow down time twice that of scattering time we should be able to observe the influence of the electron's sorroundings on it. It is analogous to a ball moving slowly along a field with dips and bumps that will determine the ball's path. We should be able to calculate exact position of the ball at a given time as we know the attributes of the ball and its environment.
But we have to factor in the influence of other electrons on this particular electron as it travels on its path. Basically it is like observing the planets when they come closer to each other the interaction has dramatic consequences on their paths even though they are not touching but their gravity and other forces play a huge dangerous game of pull and push and we can measure their position and time if we know all attributes of the interacting planets.
so I conclude with prediction that sooner or later we would be able to measure time and space simultenously and that will give us unimaginable control in creating the best performing devices.

Significance of Being Insignificant

Now and then I ask myself WHO AM I and WHY AM I,and the answer becomes egotistical ME ever proud of WHAT I AM, the material thing i have collected and knowledge i have acquired so far, I tell myself I AM VERY SIGNIFICANT INDEED. BUT when I realise that i am not the only one in my family, my SIGNIFICANCE is slightly reduced. For example in my family we are 7 and that reduces my significance even further.

As I live in the community of hundred thousand people my significance becomes even less just one out of hundred thousands, and if i factor in the city and the country population i get confused to understand What is my Purpose, WHY AM I ME. Then it hits me that if factor in the world population my significance becomes just one in six billion. if i put in all living creatures on earth my significance becomes less than a pixel on the largest screen.

Then I look out into the blue yonder and find that i leave in a galaxy of more than 200 billion suns, that reduces my signifance even more and to realise that there are more than hundrends billions of galaxies my significance becomes less than a grain of sand in all grains of sand on earth.

Then I look back and I say to myself there must be a very SIGNIFICANT reason for me to BE who I AM. The reason must be bigger than the size of galaxies put together to make my INSIGNIFICANT very SIGNIFICANT. I realise that everything else but Me follows LAWS of Physics or Nature to the letter but I HAVE A CHOICE. I can Think, I can move mountains if i want to, i can fly as far as I could into the universe, I can rearrange Nature, I can destroy species and rearrange them and disrupt the order of Natural processes I can and most of the time i am trying to even destroy the very foundation that make me SIGNIFICANT. SO Who Am I, I AM STUPID, FEABLE,IGNORANT and ARROGANT HUMAN BEING FOR NOT REALISING THE SIGNIFICANCE OF BEING INSIGNIFICANT.

Quantum Confined Stark Effect on Semiconductor devices

Quantum Confined Stark Effect can be observed in Quantum Wells due to the presence of excitonic states in the bandgap of the semiconductor structure which enhance the absorption of photons with energy lower than that of bandgap. This effect is useful in devices that uses changes induced by electroptic effects to operate. devices such as absorption modulators and even those refractive modulators benefit from QCSE effect. excitons exist in bulk semiconductor devices at very low temperature, but if you increase confinement by introducing quantum well structure excitons can exist even above room temperature. by the way excitons are electron-hole bound state which tends to lower the band energy. In Mach-Zehnder modulators the passive waveguide can incorporate QWs to enhance their refractive index change due to electro-optic effects...using materials with larger conduction band offset and smaller valence band offset one can achieve higher modulation speed and bandwidth.