Dilute Nitride: What and Why

For decades, InP (indium phosphide) based lasers have dominated the optical communication market especially for long haul. This is because it was believed that there was no other material lattice matched to GaAs (gallium arsenide) that can emit > 1.1 micron. However, InP is very expensive. As a result, the cost to setup a modern MAN or LAN is simply too high because it requires tens of millions of lasers.

Around 1995, Kondow et al have proposed a new material called GaInNAs (gallium indium nitride arsenide) which capable of emitting light at 1.3 micron. This material is also called dilute nitride because a very low percent of Nitrogen is incorporated in the material. Because this new material can be grown on GaAs substrate which is considerably cheaper than InP (InP substrate cost 3x) and has greater conduction band offset which lead to better carrier confinement hence, can operate at higher temperature, dilute nitride has become a centre of attention among researchers in the world.

Besides, the established GaAs/AlAs mirror for DBR also can be incorporated with dilute nitride to design a VCSEL because the material is lattice matched to GaAs. High power pump lasers for Raman amplifier also can be further developed due to greater conduction band offset of dilute nitride.

However, there are lots of challenges that need to be tackled before dilute nitride based devices can penetrate the market. The incorporation of Nitrogen has significantly degrade the quality of the material. Therefore, high percentage of N cannot be incorporated to push the wavelength up to 1.55 micron. It was reported that Sb (antimony) can be used to keep the material grow in 2D and allows for higher N incorporation. However, the role of Sb and how it affects the bandgap is still unknown.

Besides, the usage of different material for the quantum well barrier also has proven to help reducing the bandgap. Material such as GaNAs or GaInNAs with different composition can be used instead of GaAs barrier.

Based on current research, dilute nitride based devices are far from being optimised. This is because this technology is largely material and knowledge limited. New knowledge on growth, material fundamentals and defect in arsenide-nitride are essential to bring this technology forward.

Download illegally and get sued?

Additional stuff about news server, internet and download.

A few of my friends got a warning letter from the ISP for downloading illegal materials from the internet. This is the risk of downloading using peer-to-peer method. One thing one should know is that it is often for the copyright owners like TV stations to work together with the ISP. ISP have the internet traffic information and can identify users who download illegal materials. ISP will then provide those information to the copyright owners so that users can be warned or sued.
However, if one download using a news server, one is safer. That is because news server will not provide any information about their client activities to the copyright owners. So, news server users are safer and get faster download rate. But, one have to pay for it.

If you are inside a network such as university network, you are a bit protected. This is because, normally, university has the privacy policy which means university cannot expose any information to the copyright owners. So, what university normally do is, say to the owner, we will monitor our network and take necessary action to prevent the downloading of illegal materials. ie, university will give warning letters and worst case banned the students from using the university network.

The last thing is about VPN. When you are downloading, make sure your VPN is disconnected. Otherwise, information will go through the university network and you can get caught. This thing happened to my mate. He downloaded using his PC at home but with VPN connected, and of course got a warning letter from the university.

The bottom line is, it is not a big offense to download illegally but it is a serious offense if you download illegal materials and then seed them to others.

So, is it worth to download illegally? you decide.

PS: please see other entries about news server under 'news server' label.

Nak Tepon Mesia Murah?

Pilihan paling mudah dan murah ialah dengan menggunakan international calling card yang boleh didapati di mana2 grocery. Tapi, kebiasaannya, kualiti panggilan adalah rendah. Panggilan selalu tidak jelas dan kadang2 kita terpaksa call balik sampai 2/3 kali.

Orange juga ada menyediakan plan untuk mereka yang banyak call abroad iaitu plan Camel. Sebelum ini saya menggunakan plan ini untuk pay as you go saya. Kos untuk call ke mobile phone di msia ialah 8p per min. Kualiti panggilan sangat jelas dan tak perlu bersusah payah nak masukkan PIN number seperti calling card. Boleh call direct.

Baru2 ini, saya menggunakan 'Skype to Go' untuk call msia. Kosnya 4p per min untuk call mobile phone msia (kena beli credit Skype) + local call charge. Kalau kita menggunakan pay monthly, boleh tolak free minutes. Dengan kata lain, tiada kos untuk local call charge. Bila kita beli credit Skype, dia akan bagi local number dan kita call nombor tu untuk call msia.

Tapi, kalau penerima panggilan di msia (atau di mana2 di dunia) itu mempunyai software Skype di telefon mereka dan wireless internet, kita boleh buat panggilan Skype-to-Skype dan cara ini adalah percuma. Kosnya ialah kosong. Tapi, kebiasaanya, mak ayah kita tak ade Skype dalam handphone, jadi, 'Skype to Go' adalah pilihan terbaik. 'Skype to Go' tak memerlukan penerima dan pemanggil mempunyai software Skype dalam hp. Hanya beli credit dan boleh call dari mana2 telefon (mobile ataupun landline). Kualiti panggilan juga jelas.

Saya sangat recommend 'Skype to Go' kerana ianya murah, jelas dan boleh tolak free minutes.

Pasal telefon pula, sekarang ni network 3 ada buat offer untuk Nokia N71 pay monthly. Saya pun baru angkat satu. Itu pun sebab hp ni ada GPS, boleh browse internet, check email, bukak pdf files (walaupun lembap bila nk loading), power point, file excel dan word. Kira, kalau kita berjalan boleh buat kerja sekali. Saya ambil plan 500 mins, unlimited texts, unlimited internet dan kosnya GBP 25 sebulan (kontrak 18 bulan). Kalau nak murah sikit, ambil plan GBP 20 tapi dapat 200 mins, unlimited texts dan unlimited internet.

Untuk maklumat lanjut, boleh layari Skype to Go atau tinggalkan soalan kat ruang komen.

Sekian, terima kasih