Influence of Doping Atoms on Nonlinear Absorption, Ultrafast Dynamics and SHG Behaviors in GaSe Crystals

Öz

In this study, undoped GaSe, 0.1%Er and 0.1%Ce doped GaSe crystals were grown by using vertical Bridgman-Stockbarger technique. The nonlinear absorption properties and ultrafast charge transfer dynamics of all grown crystals were investigated by using open aperture Z-scan and ultrafast pump-probe spectroscopy techniques. The studied crystals showed nonlinear absorption at 1200nm wavelength with 100fs pulse duration. Nonlinear absorption coefficients increase with 0.1%Er and 0.1%Ce doping atoms. This behavior also leads to increasing of the free carrier densities with doping atoms and occurring of the excited states absorption. Second harmonic generation signals of the crystals were measured by fiber optic spectrometer. Second harmonic generation signals of the doped GaSe crystals shifted blue region of the spectrum as compared to the undoped GaSe crystal. According to ultrafast pump-probe experimental results, the undoped GaSe crystal indicates continuous excited state absorption signal while the doped GaSe crystals indicate saturable absorption behaviors after 2ns time delay between 630nm-650nm region corresponding to bottom of the conduction band. The saturable absorption signals indicate that the defect states which are occurred with doping atoms in crystal are localized under the conduction band. In conclusion of the experimental results, nonlinear absorption properties, frequency conversion and ultrafast charge transfer dynamics of the crystals can be controlled by doping atoms in crystals.

Anahtar Kelimeler

• Nonlinear absorption,Z-scan technique,Ultrafast spectroscopy,Semiconductor crystal

GaSe Kristali İçerisindeki Katkılandırma Atomlarının Doğrusal Olmayan Soğurma, Ultrahızlı Dinamikler ve İkinci Harmonik Üretimi Davranışlarına Etkisi

Öz

Bu çalışmada dikey Bridgman-Stockbarger yöntemi kullanılarak saf GaSe, %0,1 Ce ve %0,1 Er katkılandırılmış GaSe kristalleri büyütülmüştür. Açık yarık Z-tarama ve ultrahızlı pompa-gözlem spektroskopi teknikleri kullanılarak büyütülen kristallerin doğrusal olmayan soğurma özellikleri ve ultrahızlı yük transfer dinamikleri araştırılmıştır. Çalışılan tüm kristaller, 1200 nm dalgaboyunda ve 100 fs atma süresinde doğrusal olmayan soğurma davranışları göstermiştir. Doğrusal olmayan soğurma katsayıları %0,1 Ce ve %0,1 Er katkılandırma atomları ile artmaktadır. Bu durum aynı zamanda katkılandırma atomları ile serbest taşıyıcı yoğunluklarının artmasına ve uyarılmış durum soğurmalarının meydana gelmesine neden olmaktadır. Kristallerin ikinci harmonik üretim sinyalleri fiber optik spektrometre yardımı ile ölçülmüştür. Katkılandırılmış GaSe kristallerinin ikinci harmonik üretim sinyalleri saf GaSe kristaline göre spektrumun mavi bölgesine kaymıştır. Ultrahızlı pompa-gözlem deney sonuçlarına göre saf GaSe kristali sürekli uyarılmış durum soğurmaları gösteriyorken, Ce ve Er katkılandırılmış olan kristallerde 2 nanosaniye zaman gecikmesinden sonra iletim bandının hemen altına karşılık gelen dalga boylarında (630 nm-650 nm) doyum sinyalleri gözlenmiştir. Doyum sinyalleri, katkılandırma atomları ile kristal içerisinde oluşan kusur seviyelerinin iletim bandının hemen altına yerleştiğini göstermektedir. Deney sonuçlarına göre, kristallerin doğrusal olmayan soğurma özellikleri, frekans çevrimi ve ultrahızlı yük transfer dinamikleri kristal içerisine yapılan katkılandırma atomları ile kontrol edilebilmektedir. 

Anahtar Kelimeler

• Doğrusal olmayan soğurma,Z-tarama yöntemi,Ultrahızlı spektroskopi,Yarıiletken kristal

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