**Abstract**

InAlAs alloy was grown by MOCVD on an InP (311) substrate with different polarities. Measurements of photoluminescence (PL) and photoreflectance (PR) were performed to study the impact of the V/III flux ratio. It is discovered that the PL line was shifted to a greater energy side with the increasing excitation power density, and no saturation was observed of its related PL intensity. It is a fingerprint of type II transition emission. However, the recombination of the type II interface showed a powerful dependence on AsH3 overpressure and substrate polarity. In fact, we have noted an opposite behavior of type II energy transition shift from A to B polarity substrate in respect to V/III ratio variation. PR signals corresponding to Franz-Keldysh Oscillation (FKO) were observed. The analysis of their period has allowed one to assess the value of the PZ field in the samples. PL-luminescence measurements were performed out as a function of temperature. PL peak energy, PL intensity, and half maximum full width show anomalous behaviors. Indicating the existence of localized carriers, they were ascribed to the energy potential modulation associated with the indium cluster formation and PZ field.

**Keywords:** V/III flux ratio, substrate polarity, piezoelectric field, Franz-Keldysh oscillation, photoreflectance, photoluminescence

### **1. Introduction**

Recently, scientists have focused their interest in InAlAs/InP grown on nonconventional (n11) planes. For example, (311) A and (311) B are not acquired as compared to the used (001) surface due to their remarkable characteristics [1]. In addition, InAlAs semiconductor layers grown on (311) A/B-oriented InP substrates give several unique characteristics compared to those grown on InP (100). Indeed, in (311) plane, the strain and hydrostatic deformations are discovered to be improved compared to those on (100) plane [1–3]. The primary reasons for this are: (i) the presence of a built-in electric field, produced through the piezoelectric effect in the layer [1, 4, 5] and (ii) the difference in arsenic segregation at the inverse interface. It is expected that these factors will be heavily dependent on growth conditions such as substrate orientation, V/III ratio.

InAlAs-InP materials have attracted tremendous interest over the past decades due to a variety of potential applications such as optical, optoelectronic and

electronic devices [6, 7] due to its large direct band-gap energy, high electron mobility and the type II nature of the interface [8]. These advancement efforts were appointed by the fabrication and commercialization of a variety of devices such as Quantum cascade lasers (QCLs) [9, 10], Avalanche Photodiodes (APDs) [11] and high-electron-mobility transistor (HEMT) [12–14]. The heterostructures of InxAl1�xAs/InP have a type II transition [1, 15] which becomes a promising contender for the optical telecommunication light source. Different techniques such as Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Deposition (MOCVD) have developed this type of structure. However, the InAlAs material itself suffered from a large density of hetero-epitaxy-inherent defects [1, 6]: I Al content, (ii) phase separation, and (iii) InAlAs growth spinodal decomposition. Despite all this, the full potential of devices based on InAlAs/InP has still been obtained.

These issues are expected to be highly dependent on growth conditions (substrate polarity, V/III ratio, etc.) due to the large difference in bond energy between Al-As and In-As [15]. To date, most study work on the optical and electrical properties of InAlAs was performed on the conventional (100) planes, but little is known for the non-conventional (n11) planes. Different substrate orientations show various surface states, which are expected to influence the growth mode and even the optical and electrical properties of epilayers.

the luminescence measurements was performed out using JOBIN YVON HRD1 monochromatic and identified by a cooled Ge diode detector with a built-in amplifier. PR measurements were performed using a standard setup with the 514.5 nm line of Ar<sup>+</sup> laser as the pump light, which was mechanically chopped at 970 Hz. The probe light was acquired from a 250 W tungsten halogen lamp dispersed with a 275 mm focal length monochromatic. The reflectance signal is detected by an InGaAs

*, S1″, S2, S2*<sup>0</sup> *and S2″.*

**Samples Substrate orientation V/III ratio molar** S1 (311) B 25 S1<sup>0</sup> (311) B 50 S1″ (311) B 125 S2 (311) A 25 S2<sup>0</sup> (311) A 50 S2″ (311) B 125

*Effect of Piezoelectric Filed on the Optical Properties of (311) A and (311) B Oriented…*

PL spectra were registered at low temperature to confirm the effect of PZ-field

**Figure 1** illustrates the 10K-PL spectra of InAlAs/InP samples grown on (311) B and (311) A, respectively denoted S1 and S2. A higher energy side, both emissions at around 1.13 and 1.23 eV, for the samples S1 and S2, can be related to the interfacial defects between the InAlAs and InP layers [1, 19]. Both PL bands occur at about 0.8

and 1.03 eV for S1 and S2, respectively, on the lower energy side. A gradual InAsxP1�<sup>x</sup> layer formation at the interface between InP and InAlAs (see **Figure 2**) was explained by Hallara et al. [6]. For sample S1, an emission situated at around

To analyze the origin of the inverted interface (InP/InAlAs), we suggested a model based on arsenic segregation (some atomic monolayers) and linked the

We can conclude that the radiative recombination around the inverse interface with emission 1.03 eV for the polarity A is due to the appearance of a gradual layer for 3ML of InAsxP1�x. In this case, the arsenic content of xAs is about 40%, but in the inverted transition for polarity B, it is in the order of 70%. It is possible to estimate the band offset between InP and In0.513Al0.487As layers based on this reference [20]. In fact, the interface between InP and InAsxP1�<sup>x</sup> layers is type I, although it is type II for In0.513Al0.487As and InAsxP1�x, where the xAs content

There are two Gaussian peaks in the PL spectrum (see **Figure 1**). For the type II transition, an asymmetric band tail appeared in both S1 and S2 samples, resulting from unintentional thin strained InAs layers created at the InAlAs-InP interface [1, 18]. To explain more, this layer's smaller band gap can conduct a quantum well

and silicon photodiodes.

**Table 1.**

ranged from 0 to 0.78.

**177**

**3. Results and discussions**

*Growth conditions of the samples S1, S1*<sup>0</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.89441*

**3.1 Photoluminescence study**

*3.1.1 Effect of substrate polarity: PZ-field*

on the optical properties of InAlAs/InP (311) A/B:

1.27 eV may be related to acceptor-band recombination [1].

theoretical calculations with the experimental results.

The existence of aluminum in the InAlAs layer, therefore, prompts the existence of the In- and Al-rich clusters, which is the consequence of the non-uniformity in the alloy composition. As a result, it contributes to the undulation of the InAlAs bandgap from which the localized energy level is present. In addition, the substrate polarity [A or B] in our nanostructures alters the containment of electrons-holes by changing the strain and the existence of piezoelectric (PZ) field within the structure. Similar heterostructures such as In0.21Ga0.79As/GaAs (311) A MQWs [16] and heterostructures AlGaAs/GaAs grown on (100), (311) A and (311) B-oriented substrates [17] have seen the carrier localization phenomenon. The previous investigation will be constrained to those samples implanted at high index (11N). We have shown in our latest study [18] that the presence of localized carriers has been attributed to the energy potential modulation related to the existence of Indium clusters and PZ-field.

The aim of our chapter is to study the effect of PZ-field on the optical properties of InAlAs/InP (311) with different substrate polarity, elaborated by MOCVD. The research of their optical characteristics by PR and PL spectroscopy is a significant step to demonstrate the possibility of incorporating our structure into optoelectronic applications such as 1.55 μm devices.

#### **2. Experimental details**

The studies are conducted on InP/InAlAs/InP (311) double heterostructures, marked as S1, S1<sup>0</sup> , S1″, S2, S2<sup>0</sup> and S2″, which are cultivated at different V/III ratios by low-pressure metal-organic chemical vapor deposition (MOCVD). More information about development is summarized in **Table 1**. The source materials for the growth process are trimethylindium (TMIn), trimethylaluminum (TMAl) and (AsH3). At a substrate temperature of 600°C, an InP layer of 100 nm thickness was developed. The growth rate of InP is approximately 0.17 nm/s. A 270 nm thick layer of InxAl1–xAs was subsequently deposed. Each sample was finally capped with an InP layer of 10 nm.

The source of excitation is the 514.5 nm line of the continuous-wave Ar<sup>+</sup> laser with an excitation density of 80 W/cm<sup>2</sup> in PL measurements. Spectral analysis of *Effect of Piezoelectric Filed on the Optical Properties of (311) A and (311) B Oriented…*


*DOI: http://dx.doi.org/10.5772/intechopen.89441*

**Table 1.**

electronic devices [6, 7] due to its large direct band-gap energy, high electron mobility and the type II nature of the interface [8]. These advancement efforts were appointed by the fabrication and commercialization of a variety of devices such as Quantum cascade lasers (QCLs) [9, 10], Avalanche Photodiodes (APDs) [11] and high-electron-mobility transistor (HEMT) [12–14]. The heterostructures of InxAl1�xAs/InP have a type II transition [1, 15] which becomes a promising contender for the optical telecommunication light source. Different techniques such as

Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Deposition (MOCVD) have developed this type of structure. However, the InAlAs material itself suffered from a large density of hetero-epitaxy-inherent defects [1, 6]: I Al content, (ii) phase separation, and (iii) InAlAs growth spinodal decomposition. Despite all this, the full potential of devices based on InAlAs/InP has still been

the optical and electrical properties of epilayers.

tronic applications such as 1.55 μm devices.

These issues are expected to be highly dependent on growth conditions (substrate polarity, V/III ratio, etc.) due to the large difference in bond energy between Al-As and In-As [15]. To date, most study work on the optical and electrical properties of InAlAs was performed on the conventional (100) planes, but little is known for the non-conventional (n11) planes. Different substrate orientations show various surface states, which are expected to influence the growth mode and even

The existence of aluminum in the InAlAs layer, therefore, prompts the existence of the In- and Al-rich clusters, which is the consequence of the non-uniformity in the alloy composition. As a result, it contributes to the undulation of the InAlAs bandgap from which the localized energy level is present. In addition, the substrate polarity [A or B] in our nanostructures alters the containment of electrons-holes by changing the strain and the existence of piezoelectric (PZ) field within the structure. Similar heterostructures such as In0.21Ga0.79As/GaAs (311) A MQWs [16] and heterostructures AlGaAs/GaAs grown on (100), (311) A and (311) B-oriented substrates [17] have seen the carrier localization phenomenon. The previous investigation will be constrained to those samples implanted at high index (11N). We have shown in our latest study [18] that the presence of localized carriers has been attributed to the energy potential modulation related to the existence of Indium

The aim of our chapter is to study the effect of PZ-field on the optical properties of InAlAs/InP (311) with different substrate polarity, elaborated by MOCVD. The research of their optical characteristics by PR and PL spectroscopy is a significant step to demonstrate the possibility of incorporating our structure into optoelec-

The studies are conducted on InP/InAlAs/InP (311) double heterostructures,

by low-pressure metal-organic chemical vapor deposition (MOCVD). More information about development is summarized in **Table 1**. The source materials for the growth process are trimethylindium (TMIn), trimethylaluminum (TMAl) and (AsH3). At a substrate temperature of 600°C, an InP layer of 100 nm thickness was developed. The growth rate of InP is approximately 0.17 nm/s. A 270 nm thick layer of InxAl1–xAs was subsequently deposed. Each sample was finally capped with an

The source of excitation is the 514.5 nm line of the continuous-wave Ar<sup>+</sup> laser with an excitation density of 80 W/cm<sup>2</sup> in PL measurements. Spectral analysis of

, S1″, S2, S2<sup>0</sup> and S2″, which are cultivated at different V/III ratios

obtained.

*Perovskite and Piezoelectric Materials*

clusters and PZ-field.

**2. Experimental details**

marked as S1, S1<sup>0</sup>

InP layer of 10 nm.

**176**

*Growth conditions of the samples S1, S1*<sup>0</sup> *, S1″, S2, S2*<sup>0</sup> *and S2″.*

the luminescence measurements was performed out using JOBIN YVON HRD1 monochromatic and identified by a cooled Ge diode detector with a built-in amplifier. PR measurements were performed using a standard setup with the 514.5 nm line of Ar<sup>+</sup> laser as the pump light, which was mechanically chopped at 970 Hz. The probe light was acquired from a 250 W tungsten halogen lamp dispersed with a 275 mm focal length monochromatic. The reflectance signal is detected by an InGaAs and silicon photodiodes.
