Etching Characteristics and Surface Analysis of Molecular 

Bean Epitaxy Grown p-type Aluminum Gallium Nitride 

With Boron Trichloride/Chlorine Gasesin Inductively 

Coupled Plasma (ICP) Dry Etching

by Fred Semendy, Phillip Boyd, and Unchul Lee 

ARL-TR-3370 November 2004 

Approved for public release; distribution unlimited. 
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Army Research Laboratory 

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ARL-TR-3370 November 2004 

Etching Characteristics and Surface Analysis of Molecular 

Bean Epitaxy Grown p-type Aluminum Gallium Nitride 

With Boron Trichloride/Chlorine Gasesin Inductively 

Coupled Plasma (ICP) Dry Etching 

Fred Semendy, Phillip Boyd, and Unchul Lee 

Sensors and Electron Devices Directorate, ARL 

Approved for public release; distribution unlimited. 
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Etching Characteristics and Surface Analysis of Molecular Bean Epitaxy Grown 

p-type Aluminum Gallium Nitride With Boron Trichloride/Chorine Gasesin 

Inductively Coupled Plasma (ICP) Dry Etching 

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Fred Semendy, Phillip Boyd, and Unchul Lee 

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14. ABSTRACT 

Dry etching of magnesium doped p-type aluminum gallium nitride grown by molecular beam epitaxy (MBE) has been carried 

for the first time by inductively coupled plasma (ICP) system via the boron trichloride/chlorine (BCl3/Cl2) gas system with

variations in chuck power, ICP power, cholrine (Cl2) ratio in Cl2/BCl3 and process pressure. Processed samples were cleaned by 

standard techniques, depths were measured, and etching rates and selectivity were calculated. Surface morphology of the etched

samples was analyzed by atomic force microscopy (AFM) and scanning electrom microscopy (SEM). Etching rates were 

influenced by ICP power, and chuck power increased chlorine ratio in BCl3/Cl2 and process pressure. The increase in the 

etching rate is caused by an increased number of chloride radicals created by high inductive power and increased ion flux and 

thus, physical bombardment and chemical etching components are enhanced. In most cases, the selectivity with respect to the 

photo-resistance was higher than 1. AFM showed a smooth surface for the etched samples compared to the un-etched control 

sample. Roughness values increased initially, followed by a drop indicating the increased smoothness of the surface. Auger 

electron spectroscopic (AES) studies show that there is a reduction of intensity in the etched samples. Calculations indicated

that the gallium/nitrogen decreased slightly in the etched sample, which indicated a very small percentage of nitrogen deficiency 

because of surface-induced damage by etching. This might give rise to changes in resistance and ohmic contact formation. 

15. SUBJECT TERMS

ICP, etching, AlGaN, BCl3/Cl2

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Fred Semendy 

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Prescribed by ANSI Std. Z39.18 
iii 

Contents 

List of Figures iv

1. Introduction 1

2. Experiment 2

3. Results and Discussion 3

4. Conclusion 9

5. References 11

Distribution List 13
iv 

List of Figures 

Figure 1. (a) p-AlGaN etching rates with different RF cathode power; (b) selectivity of pAlGaN over photoresistance versus cathode power. (The process conditions are 500 W 

of ICP power, 20 sccm Cl2, and 15 sccm BCl3.).......................................................................4 

Figure 2. (a) Variations of p-AlGaN etching rates with different ICP power; (b) selectivity of 

p-AlGaN material over photoresistance versus ICP power. (The process conditions are 

300 W of chuck power, 20 sccm Cl2, and 15 sccm BCl3.) .......................................................4 

Figure 3. (a) Variations of etching rates for p-AlGaN for different %Cl2 in BCl3/Cl 2 ratio 

(the ICP power is 500 W and chuck power 200 W); (b) plot of selectivity as a function of 

Cl2 percentage in BCl3/Cl2 gas mixture....................................................................................5 

Figure 4. (a) Variations of p-AlGaN etch rates with different pressure (the ICP power is 

600W and chuck power 75 W); (b) plot of selectivity as a function of pressure. ....................6 

Figure 5. (a) Scanning electron micrographs of mesas etched at 20% Cl2 in BCl3/Cl2; (b) 

SEM of 70 %Cl2 in BCl3/Cl2 with ICP power of 600 W and chuck power 200 W...................6 

Figure 6. (a) AFM representative images of p-AlGaN ICP etched during various conditions: 

(a) an unetched control sample; (b) etched under chuck power change; (c) etched with 

percentage variations of Cl2 in BCl3/Cl2; (d) etched under pressure change.............................7 

Figure 7. (a) RMS roughness values of p-AlGaN ICP etched samples (a) under various 

chuck power and (b) etched with percentage variations of Cl2 in BCl3/Cl2. ............................8 

Figure 8. AES surface scan of (a) control sample p-AlGaN (b) etched sample. (The process 

conditions are 500 W of ICP power, 300 W chuck power, 20 sccm Cl2, and 15 sccm 

BCl3.) .........................................................................................................................................8 
1 

1. Introduction 

There is a tremendous push in technology to use III-nitrides for high temperature electronics and 

photonic devices. The ability to process gallium nitride (GaN) and related materials for 

electrical and optical device applications is highly important for the advancement of future high 

temperature and high power electronic and opto-electonic devices. Fabrication of a wide variety 

of GaN-based photonic and electronic devices depends on dry etching. Such devices include 

laser diodes (1), light-emitting diodes (LEDs) (2), hetero-junction bipolar transistors (3,4,5), 

p-type – intrinsic-n-type (p-i-n) photodiodes (6,7,8), and junction field effect transistors (9). 

Currently, aluminum gallium nitride (AlGaN) has become an important material for ultraviolet 

(UV) emitters and detectors, primarily because of the tunability of its band gap from that of GaN 

(3.4 eV) to that of aluminum nitride (AlN) (6.2eV) through variation of the AlN mole fraction 

(10). Deep UV LEDs with their potential applications in solid state lighting, biochemical 

detection, and high-density data storage have recently been a focus of intense research and 

development. In the fabrication of the III-nitride-based mesa structures, it is beneficial to etch 

through AlGaN alloys with a single etching recipe. Since III-nitride devices are based on heterostructures with a variety of compositions, it is necessary to develop dry etching conditions that 

can effectively cover the entire composition range of AlxGa1–xN alloys. Because of the relatively 

high bond energy (8.92eV/atom) of GaN, the threshold ion energy for the onset of dry etching is 

typically on the order of 25eV (11). Plasma-assisted dry processing techniques such as reactive 

ion etching (RIE), inductively coupled plasma etching (ICP), and electron cyclotron resonance 

(ECR) have shown the most promising results. Most opto-electronic devices require consistent, 

repeatable, anisotropic, high etching rates, and etching by the RIE method has been the method 

of choice. However, the wide band gap material-based devices require smooth surface 

morphology, low damage, and selective etching of one material over another. Since the plasma 

density in ICP etching is much higher, the results obtained with ICP etching are two or four 

orders of magnitude higher for the etching rates for the group-III nitrides as compared to RIE 

(12,13,14). Generally, the etching characteristics will be strongly affected by the choice of 

reactive gases, and the etching rates are often limited by the volatility of the III-nitride products. 

Halogen-based chemistries are preferred to etch gallium (Ga)- and aluminum (Al)-containing 

materials because of the high volatility of the etching products compared to fluorine-based 

products (15). Etching behavior of GaN, AlxGa1–xN, and AlN has been systematically studied in 

an ICP plasma etching with chlorine (Cl2) and argon (Ar) as the reagents (16). Smith et al., 

found that the etching rates were strongly influenced by ICP and chuck powers but insensitive to 

pressure, flow rate, and gas compositions. Etching characteristics of AlxGa1–xN grown by metalorganic-chemical-vapor deposition (MOCVD) were investigated in an ICP etching system that 

used a Cl2/Ar gas mixture (17). It was found that the etching rate increased with ICP power and 

chuck power, whereas it decreased with an increase in the Al composition. Dry etching of 
2 

undoped n- and p-type GaN films has been performed in ICP system with a Cl2/Ar gas mixture, 

and the authors have found similar etching behavior in all the GaN films (18). Dry etching with 

ICP was performed on n-type GaN with Cl2/BCl3 chemistry (19). In another study, it was found 

that the etching rates for n-type GaN samples for similar conditions were higher than the etching 

rate of p-type GaN (20). In general, etching rates of GaN are higher than AlGaN, regardless of 

plasma conditions. Al in AlGaN decreases the etching rates because of the higher bond strength 

between Al and N. The etching rate of AlGaN can be enhanced by the addition of BCl3 to Cl2

gas. However, little work has been done on the ICP etching of molecular beam epitaxy (MBE) 

grown p-type AlGaN films with Cl2/BCl3 chemistry. In this study, we report for the first time 

etching rates and selectivities of p-AlGaN as a function of BCl3/Cl2 ratio, various ICP and chuck 

power, and gas pressure with a Unaxis Versalock 700 (VLR) series modular cluster plasma ICP 

processing system. We report the etching rates during various conditions and the surface 

morphologies obtained with atomic force microscopy (AFM), scanning electron microscopy 

(SEM), and auger electron spectroscopic (AES). 

2. Experiment 

AlGaN layers were grown on c-plane, 2-inch sapphire substrates by MBE with RF atomic 

nitrogen plasma source (21). In this system, effusion cells provide flux of the group III element 

gallium and the p-type dopant magnesium. Typically, the RF source is operated at 400 W. For 

the material we used for the study (grown by SVT1 Associates, Inc.), 200 nm of AlN buffer were 

grown on top of a c-plane sapphire, followed by a 0.4-μm thick undoped GaN layer and then a 

thick layer that was graded over 0.1-μm film. Finally, 1 μm AlGaN (20% Al, Mg-doped) was 

grown on top. The as-grown layer is measured to 2.5 by 1017cm–3 at ambient temperature with 

mobility of 10 cm2

cm–1s

–1, with indium/zinc (In/Zn) for electrical contacts. Before etching, 

samples were cut into 5- by 5-mm squares and cleaned with trichloro acetylene (TCA), acetone, 

iso propyl alcohol (IPA), and deionized water and then blow dried with nitrogen. Standard 

photolithographic techniques were used with AZ 5214 to create a 1.4-μm thick photoresistance 

mask (AZ5214) containing 7-μm stripes separated by 200 μm. 

In this experiment, we used the VLR. It is a cluster-style plasma-processing system designed to 

service micro-fabrication requiring high performance, thin-film dry etching and or/deposition. 

The system contains a load module (LM), transport module (TM), and three process modules 

(PMs). Materials to be processed are mounted on a 4-inch sapphire or silicon wafer with cool 

grease for proper substrate cooling with a minute of heating at 50 oC and transferred to a 

cassette and then introduced into the LM. In all experiments, the gas pressure was maintained at 

5 mTorr, and the substrate and the electrode temperatures (T1 and T3) were usually kept at 

 1

Name of company; not an acronym. 
3 

25 oC. In this system, helium was used to produce a constant temperature for the various etching 

conditions. In all experiments, the gas flow rates were maintained at Cl2 at 20 standard cubic 

centimeter (sccm) and BCl3 at 15 sccm except when the Cl2 ratio was varied in the Cl2-BCl3 gas 

combination. 

We determined etching rates by the step heights measured with a KLA-Tencor2 P 15 

profilometer by measuring the feature depths before and after the removal of photoresistance. 

Anisotropy was determined by SEM. Surface roughness was examined by AFM before and after 

the etching of lapped samples via the tapping mode with calibrated silicon (Si) tip. Surface 

analysis was performed on selected samples by X-ray photoelectron spectroscopy (XPS) with the 

Physical Electronics PHI 5800 XPS System. 

3. Results and Discussion 

The effect of chuck power variation on the etching rates on p-AlGaN and the selectivity are 

plotted an figure 1(a) and (b). The chuck power is increased gradually in 100-watt steps, starting 

from 75 W and ending at 400 W with the ICP power maintained at 500 W. The etching rate 

increased from 1960 Å/min to 5003 Å/min at a maximum of 400 W. As can be seen from the 

graph, the etching rate increased monotonically as the chuck power increased, reached a 

maximum at around 300 W and remained almost the same around 400 W. When we look at the 

data, the etching rate was 4916 Å/min at 300 W and 5003 Å/min, showing a deceleration of 

etching rate. The initial increase in the etching rate can be explained as attributable to an 

increase in ion bombarding energy. The increase in etching rate can be attributed to an 

increasing sputter desorption of each product as well as more efficient breaking of the Ga-N 

bonds as the ion energy is increased. The selectivity is plotted against chuck power in 

figure 1(b). As the cathode power increases, the ion bombardment also increases, and as a result, 

the selectivity changes direction and decelerates and decreases with the increased sputter 

yielding of photoresistance. This etching rate is very similar to what others have obtained for 

AlGaN with Cl2/Ar gas system. They obtained an etching rate of 3020 A/min for a bias voltage 

of –250 V. 

 2

Name of a company; not an acronym. 
4 

 

(a) Etch Rate vs Chuck Power (W)

0

1000

2000

3000

4000

5000

6000

0 100 200 300 400 500

RF Chuck Power ( W)

Etch Rate ( A/min)

(b) Selectivity vs RF Chuck Power (W)

0

0.5

1

1.5

2

0 100 200 300 400 500

Chuck Power (W)

Selectivity

Figure 1. (a) p-AlGaN etching rates with different RF cathode power; (b) selectivity of p-AlGaN over 

photoresistance versus cathode power. (The process conditions are 500 W of ICP power, 

20 sccm Cl2, and 15 sccm BCl3.) 

In the next set of experiments, we examined the etching rate of p-AlGaN with the changes in the 

ICP power. In these experiments, the gas pressure was maintained at 5 mTorr, the substrate and 

the electrode temperatures (T1 and T3) were usually kept at 25 oC, the gas flow rates were 

maintained at Cl2 at 20 sccm, and BCl3 at 15 sccm, and the radio frequency (RF) chuck power 

was kept constant at 300 W and the ICP power was varied. The results of the etching rate 

changes and the selectivity changes with ICP power variations are plotted in figure 2 (a) and (b), 

respectively. 

 

(a) Etch Rate vs ICP Power

4400

4500

4600

4700

4800

4900

5000

5100

0 200 400 600 800

ICP Power ( W) 

Etch Rate (A/min)

 

(b) Selectivity vs ICP power

0

0.5

1

1.5

2

2.5

3

3.5

200 250 300 350 400 450 500 550 600 650 700 750

ICP Power (W)

Selectivit

y

Figure 2. (a) Variations of p-AlGaN etching rates with different ICP power; (b) selectivity of p-AlGaN 

material over photoresistance versus ICP power. (The process conditions are 300 W of chuck 

power, 20 sccm Cl2, and 15 sccm BCl3.) 

As can be seen from the graph, the etching rates increased with increasing ICP power. The ICP 

power was changed from 300 W to 700 W with a step increase of 100 W. For 300 W, we 

obtained an average etching rate of 4493 Å/min and 4874 Å/min for 700 W ICP power. As the 

ICP power increased, the etching rate increased because of higher concentrations of reactive 
5 

species producing higher etching rates. Because of an increase in ion flux, the bonds are broken 

more and there is an increase of sputter desorption. At higher ICP power, the etching rate 

decreases. We have observed that the DC bias voltage decreased as the ICP power increased. 

Thus, at high ICP power, the bias voltage is smaller, which will produce low ion energy plasma 

that will make the etching rate decrease at higher ICP power. The lower etching rate can thus be 

attributed to sputter desorption of reactants from the surface before they have time to react. The 

selectivity is plotted in figure 2 (b). As the ICP power changes, we see a corresponding change 

in the selectivity and we observe the selectivity increasing because of the damage on the 

photresistance initially but less pronounced for additional ICP power. 

Variation of Cl2 concentration was done in the next set of experiments to obtain etching rates and 

selectivity with respect to the percentage of increased Cl2 ratio in BCl3/Cl2. In figure 3 (a), 

p-AlGaN etching rates are shown as a function of Cl2 percentage in BCl3/Cl2 gas mixture and in 

figure 3 (b) shows selectivity. 

 

(a) Etch Rate vs Cl2 %

0

1000

2000

3000

4000

5000

0 20 40 60 80

% Cl2 in Cl2/ BCl3

Etch R ate ( A/min )

%b) Selectivity vs CL2 % in Cl2/BCl3

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70 80

CL2 % in Cl2/BCl3

Selectivity

Figure 3. (a) Variations of etching rates for p-AlGaN for different %Cl2 in BCl3/Cl 2 ratio (the ICP power 

is 500 W and chuck power 200 W); (b) plot of selectivity as a function of Cl2 percentage in 

BCl3/Cl2 gas mixture. 

The increase in Cl2 flow in the BCl3/Cl2 ratio increases the etching rate of p-AlGaN. In the 

experiment, the total gas feed rate is kept constant at 35 sccm and the ICP power at 500 W and 

the chuck power at 200 W and pressure at 5 mTorr. When the chlorine concentrations increase, 

more chlorine radicals are produced, which increases the etching rate. 

The physical bombardment changes as the chlorine concentrations and the degree of dissociation 

change, which lead to the enhancement of chemical reaction. In the dissociation mechanism, one 

can get two Cl atoms from a single molecule of Cl2 but only one atom of Cl for a single molecule 

of BCl3. As a result of more Cl atoms from Cl2, the etching rate increases. The Cl2 was changed 

to 70% in the experiment. However, as can be seen in figure 3 (b), the selectivity over 

photoresistance increased slowly with increasing percentage of Cl2 ratio and then jumped to a 

higher selectivity ratio, indicating damage of photoresistance because of increased availability of 
6 

chlorine radicals. In the next set of experiments, the chamber pressure was changed from 

5 mTorr to 25 mTorr. The etching rates were measured and the selectivity calculated, and both 

are plotted in figure 4 (a) and (b). As can be seen from the graph, the etching rate clearly 

dropped after around 15 mTorr. This decrease in etching rates is because the mean free path that 

the ions have to travel is much shorter at higher pressure than at 15 mTorr. At higher pressure, 

kinetic energy is lower, creating more collisions between ions, causing the plasma to be much 

denser. The selectivity of p-AlGaN with respect to the photoresistance also shows a similar 

pattern because of lower plasma densities or polymer formation on the surface. 

 

(a) Pressure vs Etch rate

0

1000

2000

3000

4000

5000

6000

7000

0 5 10 15 20 25 30

Pressure (mTorr)

Etch Rate ( A/min)

 

(b) Selectivity vs Pressure (mTorr)

0

0.5

1

1.5

2

2.5

3

3.5

0 5 10 15 20 25 30

Pressure (mTorr)

Selectivity

Figure 4. (a) Variations of p-AlGaN etch rates with different pressure (the ICP power is 600 W and chuck 

power 75 W); (b) plot of selectivity as a function of pressure. 

The chlorine-etched samples were studied with a SEM for surface smoothness, and the SEM 

pictures are provided in figure 5 (a) and (b). 

 

Figure 5. (a) Scanning electron micrographs of mesas etched at 20% Cl2 in BCl3/Cl2; (b) SEM of 70 %Cl2 in 

BCl3/Cl2 with ICP power of 600 W and chuck power 200 W. 
7 

At a lower concentration of chlorine, the damage is minimal and side walls are clearly defined 

with smooth anisotropy. However, at higher Cl2 percentage, the damage on the side wall is 

obvious and there is visible side wall erosion which indicates that the Cl2 component dominates 

the etching process by chemical reaction. 

The surface morphology of etched p-AlGaN was examined with tapping AFM. The etched 

samples were scanned by this technique and representative images are shown in figure 6. 

 (a) (b) 

 (c) (d) 

Figure 6. (a) AFM representative images of p-AlGaN ICP etched during various conditions: (a) an unetched control 

sample; (b) etched under chuck power change; (c) etched with percentage variations of Cl2 in BCl3/Cl2; 

(d) etched under pressure change. 

The surface roughness and the images change, depending on the way the samples were etched. 

The sampled area in all cases was 5 μm by 5 μm. The smoother etched surface in 6(c) appears to 

be related to the more stoichiometric removal of surface residue during the Cl2 etching. The root 

mean square (rms) roughness was measured with the AFM, and the results are plotted in figure 7 

for two cases. 
8 

 

(a) RMS roughness vs chuck

 power(W) 

0

1

2

3

4

5

6

7

0 100 200 300 400 500

Chuck Power (W)

rms roughness (nm)

 

(b) RMS roughness vs Cl2 in Cl2/BCl3

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60 80

Cl2 in Cl2/BCl3

rms roughness (nm)

Figure 7. (a) RMS roughness values of p-AlGaN ICP etched samples (a) under various chuck power 

and (b) etched with percentage variations of Cl2 in BCl3/Cl2. 

In the case of roughness measurements with variations in chuck power, the rms roughness 

increases first, followed by a drop in the roughness, which indicates the smoothness of the 

surface because of high chuck power. The rough sharp features are removed faster than flat 

features, thus providing a smooth surface. In the second case of percentage variations of Cl2 in 

BCl3/Cl2, the roughness increases as more and more chorine is added. However, the uniformity 

of roughness improves at a higher amount of chlorine. 

A surface study was also performed on a number of etched and a control samples with AES 

analysis with a scan voltage of 3 kV. Results are shown in figure 8. The main change is the 

reduction of both Ga and N2 signals in the etched sample. Calculations indicate that the Ga/N 

decreases by about 10%, which indicates a Ga deficiency in the etched surface. 

Figure 8. AES surface scan of (a) control sample p-AlGaN (b) etched sample. (The process conditions are 500 W 

of ICP power, 300 W chuck power, 20 sccm Cl2, and 15 sccm BCl3.) 

200 400 600 800 1000 1200 -6000

-5000

-4000

-3000

-2000

-1000

0

1000

2000

3000

120103FS103.spe

Kinetic Energy (eV)

c/s

 C1

 N1

 O2 O1

 Ga4

 Ga3

 Ga2

 Ga1

200 400 600 800 1000 1200 -6000

-5000

-4000

-3000

-2000

-1000

0

1000

2000

3000

110603FS105.spe

Kinetic Energy (eV)

c/s

 C1

 N1

 O2 O1

 Ga4

 Ga3

 Ga2

 Ga1
9 

4. Conclusion 

In this study, we investigated MBE grown Mg-doped p-AlGaN etched by inductively coupled 

plasma with Cl2/BCl3 as etching gases. A detailed study of the samples was conducted and 

reported here with variations in chuck power, ICP power, Cl2 ratio in Cl2/BCl3, and process 

pressure with a VLR series modular cluster plasma ICP processing system. From the study 

etching rates, selectivity, surface roughness, bearing analysis, SEM, and AES surface analysis 

were performed. It was found that p-AlGaN could be successfully etched by Cl2/BCl3 gas 

system. Etching rates were greatly enhanced by the rf chuck power, ICP source power, the 

chlorine concentration, and process pressure. The highest etching rates with ICP power change 

were about 5000 Å/min. The etching rate changed about 12% as the ICP power increased from 

300 to 700 W. The selectivity improved three-fold. In using different RF chuck power, we 

found that the etching rate was more than doubled when the power increased from 75 W to 400 

W of rf chuck power. The selectivity with respect to the photoresistance improved as the power 

increased. When changing the Cl2 percentage in BCl3/Cl2 gas mixture to obtain etching rates, we 

found that the etching rates monotonically increased with the increase of chlorine and the 

selectivity showed marginal improvement initially but improved substantially to five-fold after 

40% of chlorine was added to the BCl3/Cl2 gas mixture. In varying the pressure to change the 

etching rate, we found that the etching rate (even though initially increased at higher pressure) 

decreased. This decrease in etching rates can be explained as attributable to the mean free path 

changes that ions travel; the distance is much shorter at higher pressure than at 15 mTorr. At 

higher pressure, the KE is lower, creating more collisions between ions, causing the plasma to be 

much denser. The selectivity of p-AlGaN with respect to the photoresistance also shows a 

similar pattern. To find the surface morphology of etched samples, especially the ones etched by 

various percentages of chlorine, we observed that the damage on the etched samples at a lower 

concentration of chlorine is lower but at higher concentration, there is visible side wall erosion 

which indicated that the Cl2 component dominates the etching process by chemical reaction. 

The surface morphology of etched p-AlGaN samples was examined by AFM. It was found that 

the surface images changed depending on the way the samples were etched. Smoother etching 

surface was obtained with chlorine etching because of the stoichiometric removal of surface 

residue in this type of etching. The rms roughness increased first, followed by a drop in the 

roughness. This indicates the smoothness of the surface because of high chuck power and the 

rough sharp features were removed faster than the flat features, thus providing a smooth surface. 

This report documents for the first time the bearing analysis of MBE grown Mg-doped p-AlGaN 

samples. Bearing analysis indicated that the control sample had a larger bearing area, meaning 

that it has a larger surface area above or below a given height whereas for the chlorine etched 

and other etched samples, these values were lower, indicating that the etched samples are 

smoother. However, the etched samples had larger areas of uneven surface compared to the 
10 

control sample, as shown the histogram. AES studies of the control and etched samples indicate 

the reduction of Ga and N2 signals in the etched sample. Calculations indicate that Ga/N 

decreases by 10% in the etched sample, indicating a Ga deficiency in the etched sample. 
11 

5. References 

1. Nakamura, S. IEEE J. Sel. Top, Quantum Electron 1998, 4, 483. 

2. Nakamura, S.; Fasol, G. The Blue Laser Diode (Springer, Berlin. 1997) 

3. Ren, F.; Abernathy, C. R.; Van Hove, J. M.; Chow, P. P.; Hickman, R.; Klassen, J. J.; Kopf, 

R. F.; Cho, H.; Jung, K. B.; La Roche, J. R.; Wilson, R. G.; Han, J.; Shul, R. J.; Baca, A. G.; 

Pearton, S. J. MRS Jnl. Internet Semicond. Res. 1998, 3, 41. 

4. McCarthy, L. S.; Kozodoy, P.; Den Baaars, S. P.; Rodwell, M.; Mishra, U. K. 25th Intl. 

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13 

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