In The Semiconductor Light To Stimulate The Study Of The Strength Of The Nonlinear Regional Response

In this work,the excitation intensity dependent(EID) nonlinear response in semiconductor(SC) excited by femtosecond(fs) laser was studied,majoring experimental researches.Because of band structure distinctness which results in the obviously different optical properties between SC with direct band gap and that with indirect band gap,we have employed the electrical approach to investigate the Si Schottky junction excited by fs laser,while employing the optical approach to investigate the(In/Ga)As quantum dot(QD) excited by fs laser.In the preface,brief introductions for fs laser and the optical absorption in SC are given firstly.Then the research history of the surface photovoltage(SPV) in the illuminated SC,and the conception of local heating effect in the SC excited by fs laser are presented.In the following chapter 2,techniques for experiments in our work are introduced. After showing the history and principle of the fs laser,which focuses in the principle and characteristics of the Ti:Sapphire fs laser,the measuring principle of the lock-in amplifier employed in the experiment with fs laser is introduced,pointing out the difference from that employed in the experiment with continuous laser.In chapter 3,there are experimental results of EID SPV from the Si Schottky junction excited by fs laser,measured by electrical approach.From the experiment it is known that the SPV induced by the built-in potential(BP) increases with the incident light intensity,followed by that the SPV induced by the BP reaches to the saturation at high incident light intensity,then the Dember potential(DP) induced SPV takes the key role at higher incident light intensity.The ultrahigh carrier intensity induced by fs laser results in DP effect distinctly.The sign of the SPV induced by BP in p type Schottky junction is opposite to that in n type Schottky junction,while both of signs of the SPVs induced by DP in p type and n type Schottky junction are the same.Therefore the sign of the SPV induced by BP is opposite to that induced by DP in p type Schottky junction,while the signs of the SPV induced by BP and by DP in n type Schottky junction are the same.So the measured SPV in p type Schottky junction increases with the incident light intensity firstly,and after reaching to the maximum the measured SPV decreases with the incident light intensity increase,which is the representation of DP effect.But the measured SPV in n type Schottky junction increases with the incident light intensity all the time,lastly reaching to the saturation, without the distinct representation of DP effect.Moreover,under weak illumination and employing autocorrelation and SPV measurement,a new technique for measuring the characteristics(such as duration,envelop,and central wavelength) of fs laser and a new technique to detect two photon absorption coefficient in SC are introduced. Comparing with the traditional techniques,those introduced here are easily carried out, more sensitive,more applicable,less requests needed,and etc.In contrast,due to the direct band gap,in chapter 4 the EID photoluminance(PL) from(In/Ga)As QD sample excited by fs laser was investigated,measured by optical approach.The importance of wetting layre(WL) in the QD sample is discussed,and experimental results induced by fs laser are compared with those by continuous laser. From the EID PL emitted from the QD system,the local heating effect is obvious,and it is well known that the WL plays as a bridge relating isolated QDs together to enable carriers transferring easily among them.When the excited carrier intensity goes up, isolated QDs are correlated as a quasi-unite by the WL,screening the difference of QD sizes more or less.At last,a summary of this thesis are given.Based on the summary of the experimental results,the unknown fields are brought up,and the further work to explore them are also sketched out.